Answer:
What I am filled, I can point the way. When I am empty. Nothing moves me. I have two skins. One without and one within.
who do you think you know but sometimes you don't
Lighter than what I am made of, More of me is hidden Than is seen.
Turns us on our backs, and open up our stomachs. You will be the wisest of men though at start a lummox.
A kind of weather that comes your way, but add a "D" and it will run away
You use it between your head and your toes, the more it works the thinner it grows.
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?