In vedic astrology, sun represents career and soul, and gemini is the sign of communication, business ruled by mercury. Sun in gemini shows that the person will be communicative and in his career he deals with lot of communication. Communication becomes an integral part of life.
The individual with sun in gemini loves to talk about creative ideas and business. As Sun represents father, the person is communicative with father too or the father may be into business or profession related to communication. The native can also be in profession related to communication. The more they communicate, the more better for career. The native has a lot of creative ideas especially regarding business. The native loves sharing ideas with others. As gemini is a sexual sign, the native has a lot of sexual energy.
The impact of sun will depend on the position of Mercury and the nakshatra that impact the sun. If Mercury is strong the person will be logical and straightforward in conversation. If Mercury is weak the person will loose the flow of conversation midway or his conversation may not be clear to others. Whereas, if sun is in mrigashira nakshatra, sun energy will be impacted by Mars, sun in punarvasu nakshatra will be impacted by the position of jupiter and sun in ardra nakshatra will be impacted by the position of Rahu.