Pins, Forks, Overworked pieces and Mate threats.
This is the position in question. It seems very complicated but I am going to break it down for you.
First of all the knight on d5 is pinned.
Second the black queen is over worked after an exchange on f4
Third the knight on f4 covers a lot of important light squares if it was gone you could play Qd3 and after g6 the f6 and h6 squares are weak and the g3 knight can get there in two moves.
Lastly white(yes white) has to be careful of his back rank.
Use this knowledge to solve the problem. The solution is at the bottom of this post.