Poker is a card game played by two or more players against one another. It involves betting in rounds, and raising and re-raising. The highest hand wins. A hand is comprised of your personal cards in your hand, plus the five community cards on the table. You can also bluff, either by pretending to have a strong hand that will see you through to the end (and take their chips), or by pretending to have a weak hand that will cause your opponents to fold (which lets you win their chips).
In each round of betting, the player to the left of the dealer begins by placing a bet of one or more chips in the pot. Then each player in turn has the option to call that bet, raise it, or drop. If a player chooses to raise a bet, he must place in the pot enough chips to make up at least the amount of the bet made by the person before him.
As you play, it is important to learn how to read the other players. Identifying how conservative or aggressive they are can help you determine their betting patterns and predict what type of hands they will have. A conservative player will usually fold early in the hand, and a risk-taking aggressive player will often bet high on their first few turns.