Fold: You don’t put in, any more money, you leave out of the hand.
Call: You put in money equal to the amount bet. You stay in the hand.
Raise: You put money into the pot equal to the amount bet so far, plus additional money (you raise).
Reraise: Suppose someone else raises you, but you feel that you have a very strong hand. You can reraise your opponent to force him to put in another bet to stay in.
Check-raise: You want to take more than just one bet from your opponent. So you check, your opponent bets, and you raise him.
Check-call: If you have a decent hand, but you think there is a good chance your opponent might have a better one, you may wish to avoid a raise. In this case, you can check and call.
