Poker is one of the games which lies in the ‘grey area’ as there’s no ‘black & white’ law around it. While games like teen patti (flush) have been banned, playing rummy has been held not to be punishable. In 1968, the Indian judiciary declared rummy to be a ‘skilled game’ rather than ‘a game of chance’.
Games like poker may fall under the archaic The Public Gambling Act of 1867 which prohibited gambling. However, the act does not to apply to certain games, including, any game of ‘mere skill’ wherever played. Hence, one needs to clarify, basis the judicial decisions, if poker is a ‘game of skill’ or a ‘game of chance’.
Further, basis the area (jurisdiction) in which you wish to operate, you may require to comply with local acts like, Bombay Prevention of Gambling Act, 1887, Goa, Daman and Diu Public Gambling Act, 1976, Karnataka Police Act, 1963, Punjab Public Gambling Act, 1867, The Delhi Public Gambling Act, 1955, and the like.
Broadly, you may require, inter alia: (a) authorization/ permission/ NOC from the local police or the jurisdictional magistrate; (b) details of additional setup that you may need to put in place (like infrastructure, point system etc.); (c) infrastructure licences/ permits (the process may be different for online gaming); and (d) entertainment licence and payment of entertainment/ luxury tax, etc, basis your specific requirements.
Businesses like these may usually be registered as for profit private limited/ partnership/ public limited companies, subject to any case specific reservations.