arakamsa is a term mainly used in Jaimini sutra, or Jaimini astrology. In Jaimini there are seven karakas which represents different things in your life. Based on their degrees they play a certain role in the horoscope. From the highest to the lowest (7th) degree, planets are given a certain karaka name. The planet with the highest degree in the horoscope which is between 0-30 degrees, becomes the atmakaraka. Planet closest to the 30th degree is the atmakarka. This excludes Rahu, Ketu, Neptune, Uranus and Pluto. These planets are not part of the Jaimini. Once you add these plantes in Jaimini your entire prediction will be wrong.
Once you figure out which planet is the atmakaraka, look at the sign placement of that planet in the navamsa chart. This is known karakamsa: Placement of atmakaraka in Navamsa. This is sign and house placement both for D9 (Navamsa chart). Such placements give a much clear indication of the native's spiritual and professional life. Through the placement of karakamsa one can see what the soul or 'Atma' is desiring. How it wants the life to be live and viewed on this three dimensional plain. There is a lot more information on this besides this small article, but due to tremendous amount of interest in Jamini which has been invoked through my videos, I am obligated to write about it, at least what I have learned.
One thing you can see with karakamsa is the soul's ability to reach the next level of salvation or a higher frequency lokha (world). When looking at the placement of atmakarkaa in navamsa, you should see what planet is sitting in 12th from the atmakarka planet, if any. This will tell what will happen to the soul. A malefic planet like Saturn, Mars or Rahu sitting 12th from atmakarka or Karakamsa shows that souls still has many lessons to learn before elevating itself to a higher plain. If a benefic planet sits 12th from karakamsa, it shows that the soul has reached a point where it will move to the higher world after the death of physical body. Ketu sitting 12th from karakamsa means the soul will not go to any higher world, rather it will go back to the source energy and finally receive moksha, as in no longer returning to any dimenison for eternity, unless it wants to come back. This is just one way of using the karakamsa. If there are multiple planets sitting in 12th from the atmakaraka, then one with the highest degree in the birth chart takes the charge. But most of the time someone may not have any planets 12th from karakamsa, in such a case you will use the sign that sits and its lord. If the lord of that sign is melafic then sturggle in attaining mokhsa, if benefic then easy in attaining mokha.
If you look at 9th place from karakamsa it will show the luck and easyness the souls has in this to achieve it's spiritual studies and guidance from gurus. Malefic sitting 9th from the atmakraka will show a struggle to understand spiritual world, vs. benefic in the 9th from atmakarka will show that one has blessings to learn their way into the other lokha.

Effects of Karakamsa

If Atmakaraka be in Aries Navamsa, there will be nuisance from rats and cats at all times.
A malefic joining will further increase the nuisance. Should Atmakaraka be in Taurus Navamsa, happiness from quadrupeds will result. Should he be in Gemini Navamsa, the native will be afflicted by itch etc.If he be in Cancer Navamsa, there will be fear from water etc.. If he be in Leo Navamsa, fear will be from tiger etc.. If he be in Virgo Navamsa, itch, corpulence, fire etc. will cause trouble; while in Libra Navamsa, the Atmakaraka will make one a trader and skillful in making robes etc. Scorpio Navamsa holding the said planet will bring troubles from snakes etc., and also affliction to mother's breasts. There will be falls from height and conveyances etc. if it is Sagittarius Navamsa that is occupied by Atmakaraka. Capricorn Navamsa in this respect denotes gains from water-dwelling beings and conch, pearl, coral, etc.. If it is Aquarius Navamsa holding the said planet, the native will construct tanks etc. And in Pisces Navamsa the Atmakaraka will grant final emancipation. A benefics aspect will remove evils while that of a malefic will cause no good.

9-11. O Brahmin, if there be only benefics in the Karakamsa and the Navamsa of Lagna and be aspected by benefics, the native will undoubtedly become a king. Should the angles/trines from the Karakmsa be occupied by benefics devoid of malefic association, the native will be endowed with wealth and learning. The combination of benefic and malefic will in this context yield mixed results. It the Upakheta (or upagraha, vide sloka 5 ch. 32) is in its exaltation sign, or own/friendly sign, and is devoid of malefic aspect, the native will go to heavens after death.
12. If the Atmakaraka is in the divisions of the Moon, Mars, or Venus, the native will go to others' wives. Otherwise, the contrary will prevail.
13-18. EFFECTS OF PLANETS IN KARAKAMSA: O Brahmin, if the Sun is in the Karakamsa, the native will be engaged in royal assignments. If the Full Moon is there, he will enjoy pleasures and be a scholar; more so if Venus aspects. If strong Mars is in Karakamsa, he will use the weapon spear, will live through fire, and be an alchemist. Should strong Mercury be in Karakamsa, he will be skillful in arts and trading, be intelligent, and educated. Jupiter in Karakamsa denotes one doing good acts, endowed with spiritualsim, and Vedic learning. One will be endowed with a longevity of 100 years, be sensuous and will look after state affairs if Venus is in Karakamsa. Saturn in Karakamsa will give such livelihood as due to the native's family. Rahu in Karakamsa denotes a thief, a bowman, a machinery maker, and a doctor treating poisonous afflictions. If Ketu be in Karakamsa, one will deal in elephants and be a thief.

19-22. RAHU-SUN IN KARAKAMSA: Should Rahu and the Sun be in Karakamsa there will be fear from snakes; if a benefic aspects the said combination there will be no fear but a malefic aspects will bring death (through serpents). If Rahu and the Sun occupy benefic Shadvargas, being in Karakamsa, one will be a doctor treating p[poisonous afflictions while the aspect from Mars on the said combination denotes that the native will burn either his own house or that of others. Mercury's aspect, instead of that of Mars, will not cause the said effects. If Rahu and the Sun be in Karakamsa and be in a malefic's sign in aspect to Jupiter, one will burn neighboring house while the aspect of Venus will not cause such an event.

23-24. GULIKA IN KARAKAMSA Should the Full Moon aspect the Karakamsa-placed Gulika, the native will lose his wealth to thieves or will himself be a thief. If Gulika is in Karakamsa but is unaspected by others, one will administer poison to others or will himself die of poisoning. Mercury's aspect in this context will give large testicles.

25-29. EFFECTS OF ASPECTS ON KETU IN KARAKAMSA
If Ketu is in Karakamsa in aspect to a malefic, one's ears will be severed or he will suffer from diseases of ears. Venus aspecting denotes one initiated into religious orders. One will be devoid of strength if Mercury and Saturn aspect. If Mercury and Venus aspect, he will be the son of a female slave or of a female remarried. With Saturn's aspect one will perform penance or be a servant or will be a psuedo-ascetic. Venus and the Sun together aspecting will make one serve the king. Thus, O Brahmin, are told briefly the effects of Karakamsa.

30-31. EFFECTS OF THE 2ND FROM KARAKAMSA:
If the 2nd from Karakamsa falls in the divisions of Venus/Mars, one will be addicted to others' wives and if Venus or mars aspect the said 2nd, the tendency will last to death. If Ketu is the 2nd from Karakamsa in a division of Venus/Mars, such addiction will not prevail while the position of Jupiter will cause such an evil. Rahu in the said case will destroy wealth.

32. EFFECTS OF THE 3RD FROM KARAKAMSA:
A malefic in the 3rd from Karakmsa will make one valorous while a benefic will make one timid.
33-35. EFFECTS OF THE 4TH FROM KARAKAMSA:
If the 4th from Karakamsa be occupied by Venus and the Moon, one will own palacial (or large) buildings. Similar is the effect of an exalted planet in the said 4th. A house made of stones is denoted by the occupation of Rahu and Saturn. Mars and Ketu indicate a house made of bricks while Jupiter denotes one made of wood. The Sun so related will give a house of grass. If the Moon be in the 4th from Karakamsa, one will have union with his wife in an uncompounded house.

36-40. EFFECTS OF THE 5TH FROM KARAKAMSA:

If Rahu and Mars are in the 5th from Karakamsa, one will suffer from a pulmonary consumption, more so if the Moon aspects them. The aspect of Mars on the said house will bring boils or ulcers. Ketu's aspect on the said house will cause dysentery or said diseases caused by (impure) water. If Rahu and Gulika be in the house there will be fear from mean people and poison. Should Mercury be in the said house, the native will be an ascetic of the highest order or one holding staff. The Sun and Mars in the said house respectively denote one using a knife and spear. Saturn denotes a bowman in this context. Rahu and Ketu in the said house respectively denote a machinist and a watch maker. Venus in the said house will make one a poet and an eloquent speaker.

41-45. EFFECTS OF KARAKAMSA AND THE 5TH THEREFROM:
If Jupiter and the Moon are in Karakamsa or the 5th thereof, the native will be an author. Venus in the said place will make one an ordinary writer while Mercury will give still lesser effects in this respect. Should Jupiter be alone in the said house, one will be a knower of everything, be a writer, and be versed in Vedas and Vedanta philosophy, but not an oratorian or a grammarian. Mars in this respect denotes a logician, Mercury a Mimamsaka (follower of Mimamsa philosophy, one of the six systems of Hindu philosophy), Saturn one dull-witted in the assembly, the Sun a musician, the Moon a follower of Sankhya philosophy (of sage Kapila enumerating 25 true principles with emphasis on final bliss), and versed in rhetorics and singing, and Ketu and Rahu an astrologer. Should Jupiter be related to the said positions (caused by others than him), the effected stated will effectively come to pass. Some say that the 2nd from Karakamsa be also similarly disposed.

46. EFFECTS OF THE 6TH FROM KARAKAMSA:
If the 6th from Karakamsa is occupied by a malefic, the native will be an agriculturist while he will be indolent if a benefic is there. The 3rd from Karakamsa be also similarly considered.
47-48. EFFECTS OF THE 7TH FROM KARAKAMSA:

If the Moon and Jupiter are in the 7th from Karakamsa, the native will beget a very beautiful wife. Venus in the said house denotes a sensuous wife while Mercury indicates a wife versed in arts. The Sun so related will give a wife confining domestic core while Saturn denotes a wife of a higher age bracket, or a pious/sick wife. Rahu in this context will bring a widow in marriage.
49. EFFECTS OF THE 8TH FROM KARAKAMSA:
If a benefic or the planet owning the 8th from Krakamsa be in the 8th from Karakamsa, the native will be long-lived while a malefic so placed will reduce the life span. Aspect/conjunction of both benefics and malefics will yield a medium span of life.

50-56. EFFECTS OF THE 9TH FROM KARAKAMSA:
If the (9th from Karakamsa is aspected or occupied by a a benefic, the native will be truthful, devoted to elders, and attached to his own religion. If a malefic is so related as above, one will be attached to his religion in boyhood but will take to falsehood in old age.

If Saturn and Rahu are so related as above, one will betray his elders and be averse to ancient learning. If Jupiter and the Sun are so related as above, one will betray his elders and will be disobedient to them. Should Mars and Venus be so related as above, and joining in six identical vargas, a female illrelated to the native will die. Mercury and the Moon so related will cause imprisonment of the native due to association with a female not of his own. If Jupiter is alone related to the 9th from Karakamsa by aspect or by conjunction, the native will be addicted to females and be devoted to sensual enjoyments.

57-60. EFFECTS OF THE 10TH FROM KARAKAMSA:

If the 10th from Karakamsa be aspected or conjoined by a benefic, the native will have firm riches, be sagacious, strong, and intelligent. A malefic so related will cause harm to his profession and deprive him of paternal bliss. Mercury and Venus so related will confer many gains in business (or profession) and will make him do many great deeds. The luminaries so related to the 10th from Karakamsa and if be in aspect to or conjunction with Jupiter the native will acquire a kingdom.

61-62. EFFECTS OF THE 11TH FROM KARAKAMSA: If the 11th from Karakamsa be aspected by or conjunct a benefic, the native will enjoy happiness from coborn apart from gaining in every undertaking of his. If a malefic is in the said 11th, the native will gain by questionable means, be famous, and valorous.

63-74. EFFECTS OF THE 12TH FROM KARAKAMSA: If the 12th from Karakamsa has a benefic, the expenses will be on good account while a malefic will cause bad expenses. If the said 12th be vacant then also good effects (in respect of expenses) will follow. If there be a benefic planet in exaltation or in own house in the 12th from Karakamsa or if Ketu is so placed and aspected by or conjunct a benefic one will attain heavens after death. One will attain final emancipation if Ketu is in the 12th (from Karakamsa) identical with Aries/Sagittarius and is aspected by a benefic. If Ketu is in the 12th from Karakamsa and be with aspect/conjunction of a malefic one will not attain final emancipation. If the Sun and Ketu are in the said 12th the native will worship Lord Shiva.

The Moon and Ketu in the said 12th denotes a worshipper of Gauri (a consort of Lord Siva). Venus and Ketu in the said 12th denotes a worshipper of Lakshmi (a consort of Lord Vishnu) and a wealthy person. Mars and Ketu in the said 12th denotes a worshipper of Lord Subramanya (an offspring of Lord Siva). Rahu in the 12th from Karakamsa will make one worship Durga or some mean diety. Ketu alone in the said 12th house denotes Subramanya's or Ganesa's worshipper. If Saturn is in the said 12th in a malefic's sign one will worship mean deities. Venus and Saturn in the said 12th in a malefic's sign will also make one worship mean deities. Similar inferences can be drawn from the 6th Navamsa counted from Amatya Karaka's Navamsa.

75-76. MISCELLANEOUS MATTERS (up to sloka 84): O Brahmin, if there are two malefics in a trine from Karakamsa, the native will have knowledge of Mantras (sacred spells) and Tantras (mystical fomularies for the worship of deities for attainment of super-human powers). If a malefic simultaneously aspects the said yoga, the native will use these learnings for malevolent purposes while a benefic's aspect will make him use the same for public good.

77-84 1/2. If the Moon is in the Karakamsa in aspect to Venus, the native will be an alchemist and if be in aspect to Mercury he will be a doctor capable of curing all diseases.
If the moon is in the a 4th form Karakamsa and be in aspect to Venus, the native be afflicted by while leprosy; if in aspect to Mars blood and bilious disorders, and if to Ketu black leprosy. Should Rahu and Mars be in the 4th or 5th from Karakamsa the native will suffer form pulmonary consumption and if there be Moons's aspect simultaneously this affliction will be certain. Mars alone in the 4th/5th from Karakamsa will cause ulcers. If Ketu be in the 4th or 5th from Karakamsa one will suffer from dysentery and afflictions due to (impure) water. Rahu and Gulika in the 4th /5th from Karakamsa will make one a doctor curing poisonous afflcitions or will cause troubles through poison. Should Saturn be alone in the 4th or 5th from Karakamsa, the native will be skillful in archery. Ketu lonely placed in the 4th/5th from Karakamsa will make one a maker of watches etc.. Mercury so placed will make one an ascetic of the highest order or an ascetic holding staff. Rahu, Sun, and Mars respectively in these places denote a machinist, a knife user, and a spear/arrow user.

85-86. The Moon and Jupiter in the Karakamsa or the 5th therefrom denotes a writer well-versed in all branches of learning. The grade of writership will comparatively descend in the case of Venus and further in the case of Mercury if so placed as above.

87-92 1/2. PLANETS IN 5TH FROM KARAKAMSA:

Should Venus be in the 5th from Karakamsa, the native will be a poet, be eloquent, and be a poet. Jupiter replacing denotes that he will be an exponent and be all-knowing but be unable to speak in an assembly. He will be further a grammarian and a scholar in Vedas and Upanishads. Saturn in this context will make one ineffective in an assembly, while Mercury will make him a skillful in Mimamsa (one of the six chief Darsanas). Mars in Karakamsa or the 5th therefrom will make one Justice while the Moon denotes a Sankhya Yogi, a rhetor or a singer. The Sun in the said 5th will make one learned in Vedanta and music. Ketu in the said 5th will make one a mathematician and skillful in astrology. Should Jupiter be related to the said Ketu, these learnings will be by inheritance. All these as well apply to the 2nd/3rd from Karakamsa and to the Karakamsa itself apart from applying to the 5th from Karakamsa.

93-93 1/2. Should Ketu be in the 2nd/3rd from Karakamsa, the native will be defective in speech, more so if a malefic aspects Ketu as above.

94-99. If malefics be in the Karakamsa, Arudha Lagna and the 2nd and 8th from these places, there will be Kemadruma yoga; the effects of which will be still severer if the Moon's aspect be there. The effects due for these yogas will come to pass in the Dasa periods of the Rasis or planets concerned. Kemadruma Yoga will operate additionally if there are malefics in the 2nd and 8th from the Rasi whose Dasa will be in currency. The results of such yoga will also be inauspicious. If the 2nd and 8th in the chart cast for the beginning of a Dasa have malefics, then also Kemadruma prevails throughout the Dasa