Uf... i think that the answer that you can give it depends so much of the context... In some situations this spanish expressions are very informal forms... But, we can resume all of them in a salute forms...
Que pasa? (what's up)
(you cant tell what really happen or not)
not to much, here, waiting something (no demasiado, aquí, esperando algo)may be, this expresion can be the form to start a conversation...
(que tal)- (this cannot translate in the exact mean, but it something like "how are you?"
and you can give an answer like "bien"(good), "mal"(bad)
And "Quien eres" is more easy, ti means "who are you"
dont' you know who i'm im??? you don't remember?? I'm Ataulfo from Alicarnaso (for example)