A position like this is best approached visually. What do you see? Both of Black’s knights, his a8 rook, and a pawn are lined up on the same light-squared diagonal. White’s light-squared bishop can, in principle, intervene at c6. Nothing can be done with this yet, because pieces are in the way, squares and pieces are guarded, etc. The point is just to see the idea. Then you can play with exchanges, carefully visualizing their consequences to see if they help clear the obstructions out of the way and improve the targets.

White has two possible captures that might help the b5 bishop to make trouble: NxNc6 and NxNe4. In effect those possible captures are options you hold to make the board look different. If you play NxNe4, Black will play RxN, and now the board will be changed; likewise if you then play NxNc6 and Black replies b7xN. (He can’t play d7xN because after White moved his d4 knight, Black’s d-pawn became pinned to his queen. Black’s rook no longer will be protecting the queen, either, having moved to e4 to recapture during the first sequence.) Notice how two exchanges White can initiate so change the look of the board even if they don’t turn any profits themselves.

And then what would be possible? If the position were set in front of you the answer would be obvious: Bxc6, forking the rooks and winning the exchange. (Black plays RxBe3, and White recaptures RxR.)

Lesson: move order matters. There are a number of ways to look at White’s captures in the wrong order here and find nothing; capture with the wrong knight first and the sequence is ruined.