This initial section illustrates basic pins; it is principally for those who are new to the tactic. In each case the piece that imposes the pin does so in one move and then takes the pinned piece.
It's Black's turn to move in the diagram on the left. Start with White’s king; trace the lines leading away from it; look for any other White pieces aligned with it. Here White’s rook is on the same long diagonal. This means the rook can be pinned by a queen or bishop. Black has a bishop ready for the job: he plays Bd5. Now the rook can't legally move because it would expose the king to attack. No matter what White does now, Black plays BxR on the next move and wins the rook.