The current game is descended from the aforementioned ancient Chinese game, but the two versions bear little resemblance to one another.  The original Pai Gow is a cryptic and symbolic game, very difficult to learn, and was originally played with dominos. Pai Gow Poker on the other hand is quite straightforward and based on standard poker hands, with very simple rules to follow.

In Pai Gow Poker, a 53-card deck is used. The additional card, typically a joker, is a designated wild card.  The wild card may be used to complete straights and flushes, but otherwise it seen as an Ace.  Pai Gow Poker is played on a blackjack table, and up to six players can play at a time.  Similar to Blackjack, the players compete against the dealer. 
At the start of each hand you are dealt seven cards, which you must form into two hands – one with five cards and the other with two.  The object is to win money by beating both the dealer’s high (5-card) hand and low (2-card) hand.  If the player loses both hands, the dealer collects the player’s wager, and if the hand’s are split then the round is considered a push and no money is exchanged.  The only other situation which may arise is when the player and the dealer have identical hands (either high or low).  In this case the tie goes to the dealer, and it’s called a “copy”.
When a player wins a hand, there is usually a 5% commission subtracted from his winnings.  This means that if a player wagers $10, his return on a winning hand will be $19.50.  The dealer’s rake ensures that over time he will have an edge, albeit a small one.

Several online gaming sites offer the chance to play Pai Gow for both practice and for real money.