The knight is without peer as an unmasker of attacks. The reason is that a piece generally cannot unmask an effective attack if it moves in the same direction as the piece it is unmasking. Hence rooks can unmask attacks by bishops, but not by other rooks; and a queen usually can’t unmask any sort of attack, because it can move in all the same ways as any of the pieces it might uncover. But the knight doesn’t move like any other piece on the board. It jumps rather than slides. Knights therefore are equally able to unmask diagonal attacks by bishops, vertical or horizontal attacks by rooks, and attacks of either sort by the queen. Plus the knight is a piece with a relatively low value, enabling it to be sacrificed readily for other gains. If you don’t know how to use your knight to unmask attacks by other pieces, you don’t know how to use your knight.
We begin with the knight's power to uncover diagonal attacks. In the position to the left, the sight of White’s knight in front of his queen (as well as his rook) should cause immediate thoughts of a discovery; Black's queen is loose, so White will be able to play QxQ if he can find a time-consuming move for his knight to make. The classic time-consuming move—and usually the necessary one when you hope to win the queen—is a check. White has two with the knight: Ne7, which ruins everything as Black plays QxN, and Nh6, which requires Kh8 and thus wins Black’s queen a move later.