Stand:

not to be dealt any extra cards, to keep your hand exactly as it is.

Hit:

to receive extra card from the dealer. You may hit until you decide to stand or bust.

Double:

to double your bet and receive only one extra card and to stand automatically. Usually this option is allowed on two first cards only.

Split:

in case first two cards are a pair (two nines etc.) you may decide to split them into two separate hands by doubling your bet. Some casinos allow re-splitting to make up to four hands, however re-splitting Aces is forbidden at most.

Surrender:

after player was dealt his first two cards he may decide to forfeit half of his bet by giving up his hand. Early surrender is giving up before the dealer checks for a blackjack, and late surrender is giving up after he checks his hole card. Not present in all the casinos.