The basics
The object in blackjack is simply to accumulate cards with a points total as close to 21 without going over 21, going bust. Face cards (Kings, Queens and Jacks) are counted as 10 points. Aces are either 1 or 11, whichever is better for the player's hand. All other cards are represented by their number.

If the Player and House tie on the points total then it's called a 'push' and no one wins but the player gets his money back. An ace and a 10 (Blackjack) on the first two cards dealt results in an automatic win to the player paying out at 1.5 to 1, unless the house ties. A player has the right to stand at any time but obviously the closer to 21 the better.

Playing blackjack
To win all you need to do is beat the dealer without going bust. You are bust when your points total is greater than 21 and if this happens then you loose automatically whatever the dealer does. The winner between the Casino and the Player is whoever has a total closest to 21. The points total is reached by adding up the points on each of the cards in the dealt hand.

A blackjack table will typically seat about 6 players. There will either be six or eight decks of cards used depending on the casino and they are shuffled together by the dealer and then placed in the 'Shoe' which is a card dispensing box.

Before the players receive any cards players they must first place a wager and different tables / casinos have different minimum wager amounts. The players are then dealt two cards face up. The dealer deals himself one card face up, and one face down. Each player in turn then decides to either stand or take more cards to try too get as close as possible to 21 without going bust. When all the players are finished and have either stood or gone bust, the dealer turns over his down card. It is the rule that on counts of 17 or higher the dealer has to stand; on counts of 16 or lower the dealer has to draw another card and this is where the various Blackjack strategies come into play.

As mentioned before if the player makes a total of 21 with the first two cards (a 10 or face card plus an Ace), it is an automatic winning hand unless the dealer does the same. This hand is called 'Blackjack'. If Blackjack is achieved, then the player wins one and a half times the bet unless the dealer also gets Blackjack, in this case it is a tie or 'Push' and the player gets the original bet back.

The remaining non-busted players with a points total higher than the dealer win an amount equal to their bet and also get there original bet returned. If a player has a lower count than the dealer then they lose their bet. If the dealer busts, then all the remaining players who haven't already gone bust win. There are several other betting options namely Insurance, Surrender, Double Down, Even Money and Split.

House advantage (approximate, may vary with different rules)
Without basic strategy 7% average.
With basic strategy 0.5% or less.
Card counting can reverse the advantage up to 1% to the player, although with auto-shufflers now employed in most casinos card counting is almost impossible.

Some blackjack variations
Using different number of decks: all other conditions being the same, as a general rule the fewer the decks, the better for the player.

Allowing the dealer to hit a soft 17: a disadvantage to the player. It gives the dealer a chance to improve.
Allowing a double down after splitting pairs: can be advantageous to the player if used wisely.
Allowing re-splitting of Aces: a clear advantage to the player.