Pinning your opponent is when you are able to trap one of your opponent's pieces. The most common scenario is pinning a piece that your opponent has placed in front of his or her king. Picture your opponent placing a bishop in front of his or her king and you placing a rook on the same file. Now your opponent cannot move the bishop or he or she will be placed into check. It is an illegal move to put yourself into check. Now that you have learned the tactic of pinning your opponent's pieces you need to know when it is the best time to actually capture that pinned piece.
Many times a chess player will react too quickly and take the opponent's pinned piece because it seems like the right move. This is often a mistake. If you are able to pin one of your opponent's pieces you may be best served to wait to capture that pinned piece. If you react quickly and take it now, you will lose the piece that you have used to create the pin. From the example above, you would lose your rook once you take the bishop.
A better option is to wait until your opponent moves that piece. Referencing the example again, wait until your opponent moves the king before you take the bishop. Eventually, if you are patient, your opponent will move the king in order to get the bishop back into the game. When your opponent does this take the bishop. An even better scenario is making sure that your opponent has moved king so that you can capture the bishop without losing your rook. The most important concept is to be patient. Far too many chess games are lost due to players acting too quickly.