Now we turn to studies that involve creating targets for rook forks, usually by forcing a preliminary exchange. A common complication is that at the outset of the position the rook’s path to the forking square is blocked by the piece that starts the exchange; you have to be able to see that the exchange not only creates a good target but also creates an open line for the rook to reach the key square.
Begin with the position on the left. A customary way to start thinking about tactical opportunities is to ask what captures White can make and with what consequences. Here he has just one: Nxb7; the recapture is BxN. Obviously the exchange is unprofitable on its face, but imagine the board afterwards and ask what would then be possible. What loose pieces would Black have? Both bishops. What checks would White have? Re1 and Rc7, the latter as a result of the line opened by the earlier exchange. These facts can be stitched together into a fork: Rc7+ wins the bishop that would then be on b7.