Poker is a card game in which players place bets to form a high value hand. The value of a poker hand is inversely proportional to its mathematical frequency; that is, the more unusual a combination of cards, the better the hand. The player who has the best hand wins the pot.
There are many variants of poker, but they all have the same basic structure. Each player is dealt five cards. One of these is kept hidden from other players, known as the hole card. The other four are placed face up on the table. The first player to act, as designated by the rules of the particular poker variant being played, places a bet in the pot. Each subsequent player may either call (match) the bet or raise it.
A good poker player should be able to read his or her opponents. This is done by observing subtle physical tells. For example, if someone is scratching their nose or plays nervously with their chips, it can be inferred that they have a weak hand.
It is also important to know how to play from late positions. This means that you should not bet your whole stack unless you have a strong hand, and you should avoid calling re-raises with weak hands. This is because you are exposing yourself to aggression and you will likely lose if you are out of position against the aggressor.