Upon receiving his two cards the player has four options to choose from, before proceeding to play the hand. The player is allowed to double the bet on his first two cards and draw one additional card only to improve his hand. The advantage of doubling down is that the player is allowed to raise his bet after he has seen his first two cards and the dealer's upcard. The disadvantage is that he cannot draw more than one card. If the player's first two cards are of the same rank, he may split them into two independent hands, bet the same amount on each and then play them separately.
Aces receive only one additional card.
After splitting, A-10 counts as 21, and not as blackjack. Yet, some casinos do not allow doubling after splitting a pair. A late surrender means this option is allowed only if the dealer does not have a blackjack. More valuable to the player is the early surrender, which is allowed even if the dealer holds a blackjack. But the casinos seldom offer this option.