Poker is a card game that involves chance but also a lot of skill and psychology. There are many different poker variants but they all have one thing in common, betting. Players place chips into the pot (representing money) when they either think that the bet has positive expected value or want to bluff other players. The amount of money that a player bets or raises is chosen on the basis of probability, psychology and game theory.
Once the initial bets are placed the dealer deals three cards face-up on the table. These are called the flop. The players then have another opportunity to raise or fold their hands. After the flop betting round is complete the dealer places a fifth community card on the board, which is known as the river. The remaining players then show their cards and the player with the best poker hand wins.
If you have a premium opening hand such as a pair of kings or queens you should bet aggressively to make sure that you do not lose your advantage. If you do not bet aggressively you will be beaten by players who hold two pairs or better on the flop. If the flop has lots of straight cards or flush cards then you should be especially wary of holding your pocket kings or queens.