Poker is a card game where players put money into the pot voluntarily (with the exception of initial forced bets) to try and make the best hand possible. While the outcome of each individual hand involves a significant amount of chance, the long-run expected returns of players are determined by actions they choose on the basis of probability, psychology and game theory.
Players start each hand by putting in a bet of some sort (the amount varies). They then receive 2 hole cards. Once everyone has their cards there is a round of betting, starting with the player to the left of the dealer.
One important aspect of the game is reading your opponents. This can be done through subtle physical tells, but most often it is done by observing their patterns. For example if someone is betting every single street then you can assume they have some pretty weak hands and are bluffing a lot.
Always play only with money that you are willing to lose, and keep track of your wins and losses. This will help you avoid making emotionally based decisions while playing poker and keep you from getting into trouble over the long run. If you are new to the game you should also start off conservative and low stakes so you can get used to the flow of the game while observing how your opponents react. Once you have the fundamentals down, you can gradually open up your hand range as you gain confidence and experience.