The purpose of the game is to beat the bank. One should try to get closer to 21 points than the bank. If the player goes over 21 points he has lost, no matter what the bank's score is.
Face cards (Jack, Queen, King) are worth 10 points. The cards 2 through 10 are worth face value. The ace is 1 or 11 points (which determines what value approaches 21 the closest, but doesn't go over). If the dealer has the same amount as the player it is a draw.