Figure[White to move]

Don't be confused by the compression of the pieces. Just approach them methodically, asking standard questions and tracing through their answers. What does White attack? His rook on e4 attacks the bishop on e5, but the bishop is protected and there is nothing behind it. The rook on b5 attacks the pawn on c5, which also is protected—but this time there is something behind it: a rook, and it's a loose one. So the pawn on c5 is pinned. One thought is to try to take it, but the more fruitful inquiry when you see a pinned pawn is to ask what it protects. Here it protects the pawn on b4, so White takes it for free with his other rook.

For the sake of completeness, you would not want to play this until you made sure you were not setting yourself up for trouble from the passed pawn that Black ends up with on the b-file: after play goes 1. Re4xb4, c5xb4; 2. RxR, b4-b3, Black has a pawn steaming toward promotion and White has no immediate way to take it. But he has other ways to deal with the problem. For example, he can play 3. Kd3 and then meet b3-b2 with 4. Kc2. The pawn on b2 then is stuck; so long as it stays on b2 it is protected by Black’s bishop, but if it moves to b1 it gets taken. White puts the pawn out of its misery with 5. Rb5 and 6. Rxb2, a safe capture since the rook takes protection from its king. White ends up with an extra pawn and a won endgame. There are other routes to the same outcome as well. The important point is to double-check the options your opponent will have when the smoke clears.