Figure 3.2.3.4[White to move]

It starts with identification of an idea: the kernel of a discovered attack. Here you find White’s rook blocking a check by his queen. The only question is where the rook should go. It will have two moves to inflict damage, and unlike the bishop it can reach squares of either color. Naturally White would like to go after Black’s queen, and he can. But another critical feature of the rook’s powers is that it can move both horizontally or vertically, so there still is a decision to make: White can attack Black's queen with Rc5+ or Rd6+. Choose carefully. Your chief worry in executing a discovered check is that the targeted piece—here the queen—will be able to move out of harm’s way in a manner that also blocks the check. So start by considering Rd6+ and ask whether Black’s queen would have any such moves. It would; Qc4 would block the check and also lend the queen protection against QxQ from the pawn on b5. Now try the other move: Rc5+. This time the only way Black’s queen could block the check is by moving to d5 or e6—but on those squares it gets no protection and so is lost to e4xQ or QxQ. Rc5+ thus is the winning move for White.