I like this guy who I have known for a while. People say he likes me back but I am not sure. I really really like him! What should I do?

Have you guys gone out together alone or do you just see him in school (or work)?

Some guys don't mind if you ask them out, it's just your preference if you are comfortable initiating.

We haven't gone out.
I sit next to him in class though.

It's up to you if you have the courage to ask him out. (I am assuming you are old enough to date.) Otherwise, just continue to be friends until things possibly change. Don't put any expectations on him, because he might just like to flirt in class only. You can find out if he wants to do anything by asking or just giving it time. Relax about it. If you get too serious, he may start to freak out.

You become friends with him. That's the first step. The second step is to ask him how he feels, or to ask him out.

Talk to him, and see if he is friendly.