Setting up a discovered attack: threat
Besides the forcing moves checks and captures, a third application is a threat. Examples of threats are attacking a piece, a checkmate threat or threatening to promote. The goal of the threat here is again to set up a discovered attack. After preparing a battery and finding a piece to target, a discovered attack or a discovered check follows with material gain.
What do you have to do?
Set up a discovered attack via a threat (attack a piece, generate a mate threat or threaten to promote). Afterwards, win material by performing the discovered attack or discovered check.
The battery with Bd2 and Rb2 is ready. However, you need to target enemy pieces to do something with this battery. With 1.e4 white chases the black rook to f2 (1...Rxf2). The only alternative is 1...Nxe4 to save the rook after 2.dxe4 with 2...Rf6, but in that case white has won a knight against a pawn.
After 1...Rxf2 there are three pieces on one row. The black rook is now indirectly attacked by the white rook; now to find a second piece to target. There is one! With white's 1.e4 the c1-h6 diagonal has been cleared. With the discovered attack 2.Bh6+ white gives a check and the rook on b2 attacks the rook on f2 directly. The check must be cancelled, after which white captures the rook on f2.
