Composition and Inverses of Functions

I really don't know what all of this hoo-ha means, but a student at The University Of Georgia asks:
What is Function Composition? How can you prove a function is an inverse?

In his essay he writes:

Think of an assembly line. You are being brought a new Xbox. Your job is to place the Xbox jewel on the front of the machine. Then, you send to the next person to place the back on the machine. And then, on down the line until it is ready for purchasing by the consumers. If you think of these operations as functions, then you can imagine the composition of functions.

Read the rest of his paper HERE

I got a kick out of the fact that he referenced xbox and the manufacturing of xbox's in a college paper. I hope he got a good grade!