For example, you might be playing a no-limit game with blinds of $1 and $2 and $80 in front of you. Before the flop one player has called and another raised to $10. Here you can fold, call the $10 or reraise any amount up to your remaining $80. Let's say you decided to raise to $80. When you bet all your chips like this you are said to be going all-in. Now let's imagine that everyone folds except the original raiser, who calls the $70. Since there is no more betting to be done, the flop, turn and river are now dealt and there is a showdown. If you win the hand you have more than doubled your money (known as doubling through), but if not you will either have to dig into your pockets for more money, or call it a day.
The other popular betting structure in poker is known as pot-limit. As the name suggests, in pot-limit you are allowed to bet anything up to and including the size of the pot. If someone has already bet, you calculate the maximum raise by adding up the pot to take into account the fact that you must first call their bet. Thus if the blinds are $1 and $2 and one player has already called the $2, your total maximum allowed bet is $9 ($2 for your call and $7 for your raise, since the pot size is calculated as if you had already called: $1+$2+$2+$2). The next player now has the option of either folding, calling or making a further raise themselves, up to the size of the pot. Unless you are going 'all-in', your minimum raise in both no-limit and pot-limit poker is equivalent to the bet which preceded it. Thus if your opponent were to bet $5, you can call the $5 or raise to a minimum of $10. You cannot raise to $8, since then the raise would only be $3, which is lower than your opponent's bet.
When you are playing no-limit or pot-limit poker, it is important to announce 'raise', and to then state the amount you wish to bet, before placing any chips into the pot. You are not allowed to place chips in the pot and then go back to you stack to add more. In that case you may be called for a string-raise and be prevented from carrying out your bet. This is to prevent players from placing chips in the pot, gauging their opponent's reaction, and then deciding whether or not to add more chips.
Cardrooms usually make their money by taking a cut (or rake) out of every pot. This may only be $1 for a small pot, but then increases with the size of the pot to a typical maximum of $4.
If you run out of chips during a hand you are said to be 'all-in' and can only win what is in the pot to that point. Once the other players have matched your bet this sum is set aside by the dealer as the main pot. The other players are still entitled to keep betting, but that sum will be placed in a side pot. The all-in player is only eligible to win the main pot, while the side pot goes to the player with the best hand among the other players. If that player has a better hand than the all-in player then he scoops the lot.