what is the difference between hyperbole and metaphor?
A hyperbole is an exaggeration of something, but a metaphor is comparing something (not necessarily an exaggeration).
She's as skinny as a toothpick.
Obviously, the girl is not as skinny as a toothpick, however, it is being used to show that she is extremely thin.
She is a big baby.
Here you are comparing her to a baby, not because she is one, but because she may act like on at times.
A hyperbole is an exaggeration not to be taken literally for emphasis or effect.
That sweater shrunk 10 sizes at least. (OK, the sweater probably shrunk, but I doubt it shrunk that many.)
A metaphor is a comparison between two unrelated objects. For instance, beating a dead horse to mean that something has been said or done too many times.