What does it mean when a girl puts her head on your shoulder?

Answer 1

It means that the girl like you a lot of that they trust you very much and feel safe and secure around you. I do this many times my buddy, and its because i feel like I can tell him anything and would still protect me.

Answer 2

That you are a lucky girl

Depends what gender you are, first. If you're male, it could means being friendly or tired, but can also be flirting with you - same thing apply for a female but usually more to the flirting side.

Answer 3

He needs to feel safe & secure.