At this stage each player plays out their hand with the dealer playing last. Their options are below
Stand: The player can stand meaning no more cards are dealt to the player.
Hit: The player may hit and he receives another card.
Double: The player doubles his bet and receives one more card. If he wins he will double his payout or double his loss if he looses.
Split: If the first two cards are of the same face value (or point value in some rules) then the player my split his hand. The two new hands must have bets equal to the original and are played out individually. Some casinos allow multiple splits and may or may not allow doubling after splitting.
Surrender: Not always available, this option allows the player to surrender his cards and half his bet if he doesn’t like his chances when seeing his first two cards. If the player can only surrender after the dealer checks for blackjack then this is known as a late surrender. If the player can immediately surrender this is known as early surrender which I have not seen on any online casino to this date.
Once all players have played each of their hands the dealer plays out his. The dealer will follow a set of rules which means he has no free will to take advantage of knowing what the players hand is. The most common rule is that the dealer will hit on any combination below 17, and stand on 17 and above. Other variations including hitting on 17 and hitting on a soft 17.