The object is to have a hand with a total value higher than the dealer's without going over 21. Kings, Queens, Jacks and Tens are worth a value of 10. An Ace has the value of 1 or 11. The remaining cards are counted at face value.
A basic betting strategy is simply to double the bet after losing a hand, also known as the Martingale system. This can go for multiple hands in a row until you win at blackjack. Then, you reset the bet to the starting value. That one bet will cover your previous losses and even provide a profit.