Basically means go ahead or do whatever you want with it or take as much as you can. Often used when refering to food.
P1: Do you want these chips?
P2No, go nuts
The phrase, "Go Nuts" comes from pornography where the girl giving head to the guy goes all the way down to the base of the cock.
Deepthroat. Balls Deep.
Come on, baby, Go nuts. Aww yeah, that's it! Swallow my cock.