ça va = how are you?

(litterally = "it's going?")

Tu es qui ? --> casual

Qui es-tu ? --> formal

Notice the Subject/Verb inversion.

Casual --> Subject + Verb + Qui

Formal --> Qui + Verb + Subject

et lui = and him

c'est = it is or this is or that is

C'est qui ? = This is who?

= Qui c'est ? = Who this is?

= Qui est-il ? = Who is he?

The 3 questions above are almost the same!