Poker has many families of variations: Straight (e.g. 3-card brag), Stud Poker (e.g. 7-card stud), Draw Poker (e.g. 5-card draw), Community Card Poker (e.g. Texas Hold'em).
Beginning: Every player on the table post an "ante": a forced bet required in which all players put an equal amount of money chips (usually the smallest value) into the "pot" before the deal begins.
First Betting Round: The first player is usually the player who was dealt the first card. He/she can "bet" (place the first bet of any value) or "check" (pass the decision onto next player).
After everyone plays, who still has a turn will have this additional option: "Raise": put more than the last player put in the pot. If someone "raises", then everyone must "call" or "fold".
Second Betting Round: As before, the players can either "bet" or "check", until someone places the first bet, after which players can "call", "raise" or "fold". In this phase, "fold" is more common.
The player who was dealt the first card is the new dealer, and all begins again: all post an ante, deal cards, then first betting round, next the draw, then second betting round and the showdown.
The first player to the dealer's left posts a Small Blind (e.g. same value of an ante) and the next player in turn posts a Big Blind (e.g. 2 times an ante).
After cards are dealt, play begins with third player from dealer, who must either "call" the Big Blind, "raise" or "fold". When the betting returns to the Small Blind player, he must equal the bet too