What does it mean when a boy asks you to the movies?

It can mean any number of things.

It could mean that the guy likes the girl as more than friends.

It could mean that the guy likes the girl as a friend.

It could mean that the guy wants to spend more time with the girl.

It's hard to know specifically without more details.

Just pay attention to how the guy acts around the girl and that will give you clues as to what it means. (i.e. Does he pay for her? Buy her concession stand food? Compliment her? Ask her to do other things? Include other people when they hang out?