You see White’s bishop masking his rook; you see that the rook would attack Black’s queen if unmasked; you look for a move by the bishop that would take advantage of the situation. The bishop's only capture, Bxh6, would be of no great concern to Black. But look as well for threats White can make that would have to be taken seriously. Again White can use the bishop to threaten Black’s rook, this time with Bf4. After Black moves his queen to avoid RxQ, White takes the rook and wins the exchange.
Most often the point of a discovered attack is that the unmasking piece—the bishop in these examples—is sacrificed or creates a time-consuming threat so that the unmasked piece can capture an enemy target. But here the unmasked piece (the rook) creates the time-consuming threat, effectively allowing the unmasking bishop two moves: one to line up against Black’s rook, and the other to take it. Whichever piece plays the primary attacking role, the logic of the tactic is the same: you launch two attacks at the same time, leaving your opponent time to deal only with the more pressing of them. Soon we will give more detailed consideration to the most important positions where the stationary piece does the distracting and the unmasking piece does the attacking: the discovered check.