A card's value is equal to the number on it. Face cards are worth ten, and aces are worth 11 or 1 (whatever is more beneificial). Your total is the sum of the values of all your cards.
If your hand has exactly two cards with the same value (i.e. 2 queens and nothing else), you may split. Splitting creates a new hand (with the same wager) using one of the cards. Your original hand and the new hand will each draw a card, ending with two total.
If your hand has exactly two cards, you may double down, which doubles your wager, draws one card, and then stands.
The dealer starts with two cards, one face down.
Once you stand, the dealer hits until their score is at least 17
Highest score under 22 wins. Dealer usually wins ties.
If your cards in a 2-card hand make a blackjack (total of 21), that's a natural blackjack and wins unless the dealer also has a natural blackjack, in which case it ties.
If a hand gets a (not natural) blakjack and the dealer gets blackjack, the hand ties.
If a hand goes over 21 (bust), is loses. If all hands bust, the dealer doesn't play.