Relacionarse
 

How can I say como te relationas con tus amigos, con tus compañeros de clase etc...

I referred to the dictionary on this on, and I believe the best translation would be to keep on contact with, or to make contacts with.

You certainly wouldn't use to have relations with, as this means to have romantic connections with.

@Poli: I think this expression is more about the rapport someone has with other people.
The question "¿Cómo te relacionas con tus compañeros/amigos...?" might probably be "how do you get along with your classmates/friends...?"

and Have relationships with your friends?

How are your relationships with your friends? It sounds weird to me.