Use of pin (2 moves)
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If you capture a piece that is protected by a pinned piece, the capture will force the protector to move out of the pin, and you can win the piece that is exposed behind the protector.
The black knight on b4 is protected by the knight on c6, which is pinned by the white bishop on f3 against the unprotected bishop b7.
White can use the pin to win material with Nxb4.
If black recaptures with Nxb4, White can win the exposed bishop with Bxb7.
Sometimes using the pin can involve a temporary sacrifice, as in the following example:
The white rook on e6 is protected by the pawn on d5, which is pinned by the black bishop on b7 against White's queen on f3.
Black can use the pin with the temporary queen sacrifice Qxe6!
If White captures the queen with dxe6, Black can regain the queen with Bxf3.
The investment was a good one, as after gxf3 Black will be an exchange up in the endgame, and should eventually win.