If you've never played blackjack, or need a refresher I recommend you to check out the blackjack rules.
When you arrive at the main screen, you will see a circle in front of you on which you can place a bet. Bets as much as you want, then click to deal. You will receive two cards face up and the dealer will receive two cards, one face down one face up. You will now have the option to hit or stand, and in some cases to double or split.
Your objective is to get closer to 21 than the dealer without going over. If you go over you lose instantly even if the dealer also goes over. Therefore, if you think the dealer is likely to go over, you should not take a hit. If you do not, and you do not think your total is high enough, you will hit. If not you will stand.
You can hit as many times as you like unless you go over. If you like, you can double, putting up an amount equal to your original bet and getting a single additional card. If you have two cards of the same value, you can put up another bet and split, using each of your original cards as the basis for a new hand.
Remember that each card is worth its face value, except that face cards are worth ten and aces are worth one or 11. If you get an ace and a ten-point card on your first two cards, you have blackjack and win 3-to-2 on your money unless the dealer also has blackjack.
If the dealer has an ace showing, you will have the opportunity to take insurance. For an additional half a bet, you break even on both bets if the dealer has blackjack. The odds are against you with this bet and it should be avoided.