Let's see is how the betting in poker works.
The betting round
Each poker hand is made up of a number of betting rounds. The number of betting rounds depends on the poker variation. In Texas Holdem there are four betting rounds, in Seven Card Stud there are five, and in Five Card Draw there are just two betting rounds.
Fold, call or raise
In each betting round, the betting moves clockwise around the table. Each player in turn must either match the bet of the previous player (call) or get out of the hand (fold).
Or, instead of just calling, when you're in turn to bet you can also choose to bet more than the previous bet (raise).
When all players have either folded or called the last raise, the betting round is over. All bets that have been made during the betting round are added to the pot.
All players who remain in the hand have now put in the same amount. They have all matched the biggest bet in that betting round. You can think of this as a negotiation - players agreeing on the price to see another card.
When the betting round is over, if all players except one have folded, the remaining player wins the pot. If everybody folds, you don't even have to show your cards to win. That's what makes bluffing possible n poker.
Or check, if no one has bet
Before a bet has been made in the current betting round, the player in turn can choose not to bet (check). Checking simply means passing on the turn to the next player without making a bet.
If it helps, you can think of checking as calling a zero bet. It it doesn't help you, please just forget about it.
Let's say that a player checks and another player puts in a bet. When the betting comes around to the player who checked, he may either fold or call - or raise! If he raises here, his move is called a check-raise. This is not really a rule, but it's still good to know what check-raising means.
Small blind and big blind
At the start of each poker hand, some players have to make a bet even before the cards are dealt. This is to create a small pot to compete for.
Without those "forced bets" all players could fold every hand without any cost, and poker would probably be a very slow game.
In some poker variations, the forced bets are called blinds. The player to the left of the dealer puts in the small blind, and the next player in turn puts in the big blind. This is how it works in Texas Holdem and Omaha.
Blinds are "live bets", which means that they count as valid bets in the first betting round. Once the cards have been dealt, it is the player after the big blind who starts the betting (he or she is 'under the gun'.)
He or she must either match the big blind, fold, or raise. Checking is not an option, since the big blind is considered as a valid bet. Remember that you can only check if no player has before you bet in that betting round.
Big blind has an option
Normally in a betting round, when all players have either folded or called the current bet, the betting round is over. However, when you play with blinds there is an exception to this rule in the first betting round.
In the first betting round of Texas Holdem or Omaha, if all players fold or call the big blind, the player in the big blind has an option: He or she may either check or bet.
Antes instead of blinds
Some poker variations use antes instead of blinds. An ante is a forced bet that all players have to put in the pot before the cards are dealt.
As opposed to blinds, antes are not live bets. They are just put in the middle to stimulate the betting, but do not count in betting for any one player.
When there are no blinds, there must be some other rule to decide who begins the betting. In Seven Card Stud, the player with the lowest card showing must start by putting in a half or a whole small bet (called bring in).
From there, the betting goes on a usual. Since there's no big blind, there's also no big blind option in the first betting round.
When the last betting round is over, if two or more players remain in the hand there is a showdown. Players show down their cards and the best hand wins the pot. If several hands are equally good, the pot is split equally between them.
First you must decide who will show first. If the pot was raised, it's the player who put in the last raise. If there was a bet but the pot wasn't raised, it's the player who put in the first bet. If there was no betting, it's the first remaining player to the left of the dealer.
The player who shows first has to show down his or her cards. Then the other remaining players show their cards in clockwise order. If their hands are losing, they don't have to show their cards, but you can always show your cards if you feel like it.