Answer:
I am needed for most animals and hardcover books
What can fill a room but takes up no space?
I have to be broken before I can be used
You find me behind the stars; or in a sixth seventh or third. It takes something round a computer and me to make pie. I am bigger than anything you can think of.
I am the key that is the hardest to turn
Runs over fields and woods all day. Under the bed at night sits not alone, With long tongue hanging out, Resting at your feet until we go for a walk