Answer:
I start new then become old. Start clean but become dirty. I usually start big then become little. What am I?
What loses its head in the morning but gets it back at night?
I can point in every direction but can't reach the destination by myself. What am I?
While you were folding a letter you got me. Usually you will do whatever it takes to avoid me but now you can't help but find me.
So simple, that I can only point. Yet I guide men all over the world.
It has no top or bottom, but it can hold flesh, bones, and blood all at the same time.