Poker is a card game in which players place bets on the value of their hands of cards. The player who is left with the highest ranked hand when all other players have dropped out wins the pot, or the total of all bets made during that hand. The game is normally played with 5 or 6 players.
Each player is dealt 2 cards face down and then a third card is dealt face up. There are then a number of betting rounds. Each time a player makes a bet they must either call it (match the amount of the previous bet) or raise it. Alternatively, they may fold.
Before the first round of betting begins two mandatory bets are placed into the pot by players to the left of the dealer. These are called blinds and they create an incentive for players to play.
Once the flop is revealed there are another round of betting. Once again, each player must choose whether to check (no bet) or raise (put in more chips than the previous player). They can also fold (drop their hand and not participate in that hand).
Once you understand how to read other players you can start to make money. The easiest way to do this is by putting them into categories based on their style of play. For example, if they raise pre-flop from early position then they are probably tight and aggressive. However, if they call and check a lot then they are likely more passive.