The queenside cluster of White’s pieces looks knotty, but there is nothing difficult about it if you ask the right questions. We are focusing on attacking ideas with bishops, and for Black there is just one: BxN, forking White’s bishop and queen—a small triangle. Of course the White bishop first needs to be traded in for a better target through capture by another Black piece; hence 1…. RxB; 2. RxR and now BxN forks White’s rook and queen. Targeting the White queen works because Black has protection from its own queen at c4.

Are you satisfied with this? You should not be. Remember that when you fork two pieces that aren’t the king, one of them can move to protect the other. So think especially carefully about what your opponent’s best move will be in reply. Here White can respond to the fork with Qc1, protecting the rook. The sequence still would be profitable since Black would have picked up the knight on c3, but keep pushing for ways to go farther; after White’s queen moves to c1, rethink the board. White’s rook is attacked once and defended once. If Black could add his queen to the attack against the rook then on b2, he would have it. He needs a way to do that without giving White time to move the rook out of danger. He therefore maneuvers the queen into position with a time-consuming (for White) check: Qd4+. (This is safe because we're assuming that White's queen has moved to c1.) White has to move his king; and now BxR wins the rook at no cost because Black’s queen protects against a recapture. (White’s better option after the forking move BxN is to play Qxd6, at least taking a pawn rather than making futile efforts to save his rook.)

Incidentally, at the outset of the position Black might be tempted to play BxN; once White recaptures on c3 with his bishop, the way is clear for Black to take White’s loose rook on b1 with RxR+. But the idea fails because that recapture by White—BxBc3—is a check. You cannot be too alert to possible checks your opponent can give in the midst of a plan you are devising. A check has the power to stop a tactical sequence in its tracks.