White follows the lines out from Black’s king and sees two pieces on the king’s rank: the queen and bishop. White’s rook already is on the scene; indeed, it currently pins the bishop to Black’s queen. (This is a relative pin, since the bishop is pinned to a piece other than the king; for now just see that the bishop is immobilized and that White needs a way to exploit this.) The bishop is guarded, so White can’t play RxB. What White needs is a pawn attack against the bishop. White has pawns on the right files—at c5 and e5. But their path to the pinned bishop is blocked by Black pawns. What to do? Handle it the same way we normally handle pawns that block needed paths: capture something that one of the pawns protects. Here the pawn on e6 protects the rook on f5, which White can take with RxR. After Black replies e6xR, the line is clear for White to play the pawn push e5-e6.
Now notice a side consequence of e5-e6: the path between the two queens has been opened as well. But if Black plays QxQ, White recaptures NxQ—and the bishop at d7 remains pinned. White takes it next turn. Notice, too, the importance of the move order. After Black’s QxQ, White must not play RxB+. This might look tempting, since the priority of check suggests that after Black fends off the attack on his king, White still will have time to take Black’s queen. But Black fends off the check precisely by playing his queen back to g7. White takes it with his rook, but loses the exchange once Black recaptures KxR.
Once again there are a few lessons to observe here. The first is the same as in the previous position: don’t give up lightly on the possibility of attacking a pinned piece with a pawn. Second, this position shows how pawns whose paths are blocked may be able to advance if the blockers are lured out of the way by other attacks you launch. Third, when you are pushing pawns be mindful of the lines—and especially the diagonals—they open and close as they move forward. This really is an application of the principles studied in the section on discovered attacks. In effect the pawn here unmasks a discovered attack by moving to e6, and at the same time it exposes its own queen to attack.