Procedure
Players in a poker game act in turn, in clockwise rotation (acting out of turn can negatively affect other players). When it is a player's turn to act, the first verbal declaration or action he takes binds him to his choice of action; this rule prevents a player from changing his action after seeing how other players react to his initial, verbal action.
Until the first bet is made each player in turn may "check," which is to not place a bet, or "open," which is to make the first bet. After the first bet each player may "fold," which is to drop out of the hand losing any bets they have already made; "call," which is to match the highest bet so far made; or "raise," which is to increase the previous high bet.
A player may fold by surrendering his cards. (Some games may have specific rules regarding how to fold: for example in stud poker one must turn one's upcards face down.) A player may check by tapping the table or making any similar motion. All other bets are made by placing chips in front of the player, but not directly into the pot ("splashing the pot" prevents other players from verifying the bet amount).
Read more about this topic: Betting In Poker