Usually only a bet and three raises (or four raises) are allowed on each round of betting. Most cardrooms have a limit on the number of bets and raises allowed. Of course, whenever you raise, the original bettor has the option to reraise, putting the onus back on you to match his bet to stay in the hand. However, if you particularly like your hand you may also raise, forcing the original bettor to match your raise if he wants to continue in the hand. A call involves matching the amount already bet in order to see the next card (or to see the showdown, if the last card dealt was the river card). In that case you may either call or raise. However, let's assume that you do want to continue in the hand after someone else has bet. It cannot be retrieved even if you were to realise that your hand had been discarded by accident. Having touched the muck, your hand is now dead. Once you have folded your hand it is placed in a pile of other discarded hands (known as the muck) by the dealer. Any money that you have already contributed to the pot is lost.
If you do not like your hand you can fold, relinquishing your cards and taking no further part in the hand. Let's start with your options when someone has already placed a bet (known as opening the betting).
In poker there are only five different betting actions to remember, depending on whether or not anyone has already made a bet on this round.
