In some games the pot is split between the highest hand at the table and the lowest hand. These games include Omaha 8 and Stud 8. And in Razz, the pot is awarded to the player with the lowest hand at the end of all rounds of betting.
Most of poker games are played with 52-card deck. There are 13 cards (from deuce to Ace) and four suits (heart, spade, diamond, club).
All poker games also feature a mandatory bet of some kind. In stud and draw poker games, this is usually called an "ante" and is wagered every hand. In holdem games, this is usually called a "blind" and is wagered when it's the player's turn to post the blind. Some holdem games have antes in addition to blinds.
All poker games feature one or more betting rounds in which the player can make one of the following betting choices:
Another option a player has when no one else has bet before him is to bet. Every player after the bettor has to choose to fold, call or raise. A player can't check once someone else at the table has bet into the pot.
Folding means giving up any chance of winning the pot, but it also means the player doesn't add any money to the pot. A player who folds is out of action until the next hand is dealt.
To call a bet is to put enough money in the pot to match the bettor's bet. If it's the final round of betting, the person who bet originally has to show his hand to the caller.
To raise a bet is to put more money into the pot, so that the original bettor has to add more money to the pot to stay in the hand. Someone who bets and is subsequently raised by a player later in the betting round also has the option of folding.
When the betting rounds are complete, if there are multiple players still in the pot, there is a "showdown", where the remaining players show their hands to each other. The person with the best hand wins the pot. If there is only one person left in the pot at the end of a betting round (i.e. everyone else folds), that person does not have to show his hand, and he automatically wins the pot.
Poker games are almost always played using a tradition called "table stakes", which means that only the chips that are on the table can be used to bet during a hand. A corollary to this "table stakes" rules is the "all-in" rule, which says that a player doesn't have to forfeit his stake in a pot just because he doesn't have enough chips to cover a bet or a raise. If all of a player's chips are in the pot, he's considered all-in, and additional bets and raises from other players after he is all in go into a side pot. The all-in player has no stake in the subsequent side pot, but does have a chance to win the pot he has a stake in.
There are hundreds of poker variations that are played both online and off. The most popular poker games are Texas Holdem, Seven Card Stud, and Omaha games, as well as variations like Razz and HORSE. Each variant has its own rules variations, but the betting basics are essentially the same from game to game.