Compare your cards to the dealer's: If the dealer's hand exceeds 21, all players with 21 or less win. If your hand is higher than the dealer's, without exceeding 21, you win. If you have the same total as the dealer, it's a push even if you got blackjack.
Naturals. If a player's first two cards are an ace and a "ten-card" (a picture card or 10), giving a count of 21 in two cards, this is a natural or "blackjack." If any player has a natural and the dealer does not, the dealer immediately pays that player one and a half times the amount of their bet.