There is no single version poker, instead there are many variations. All of them are generally played with a standard deck of 52 cards. A standard deck consists of of thirteen different ranks
of cards, and they are: Ace, King, Queen, Jack, 10, 9, 8, 7, 6, 5, 4, 3, 2. Each of these cards comes in four different suits:
Clubs, Diamonds, Hearts, Spades.
Some games make use of a joker or a "wild" card, but you will not find these games dealt at casinos. They are likely to be found in home games.
Poker games involve rounds of betting into a common fund, or "pot", and rounds of replacing/receiving cards. The number of
betting rounds and card draws depends on the particular variation of the game you are playing. Action proceeds in a clockwise direction.
Texas Holdem is the game of choice these days, so if you're interested you can check out the rules for texas holdem. There are also rules for other specific versions of poker on the poker variations page.
In general, players either ante, or make blind bets into the community pot. Then they are dealt cards, and a round of betting takes place. At the end of a round of betting, everyone has to have contributed to the pot equally.
When it is a player's turn to act, they may choose from the following actions:
Check - if there is not bet already on the table, the player may in essence bet 0, and pass the action on to the next player.
Call - if there is a bet on the table, the player may choose to match the bet.
Bet - if there were no bets on the table, the player places one by betting.
Raise - If there was a bet on the table,
the player may increase the bet by raising.
Fold - the player does not choose to match the bet on the table, and they forfeit any chance at winning the pot. They also surrender their cards.
The betting round ends when all players have contributed to the pot equally.
Then the next card action takes place, and that action depends on the version of poker you are playing. In Stud style games, an additional card is dealt to each player. In Draw style games, players are given a chance to discard from their hand, and receive a fresh replacement card from the dealer. In "community card" games, like Hold'em, the dealer will turn over the next card(s) to be displayed.
Betting rounds and card actions alternate a set number of times, depending upon the game.
Once the betting rounds and card dealing is completed, the Showdown takes place. In most games, the highest hand at the Showdown wins. Check my High Hand Ranks Chart for a list of which hands rank higher than the others.
If you are playing a "lowball" or "split-pot" poker game, a portion (if not all) of the pot is awarded to the lowest hand at the table. For low card rankings, see the Hi Lo Hand Ranks page.