Grammar

What are you saying? It means what are you trying to tell me? What do you mean? It's not that I didn't hear you, but I don't understand the meaning of what you're trying to tell me. You might here this if the person is asking you to be more direct. 

What do <em>you</em> saying? What do you say? means tell me what YOU think. I think we should go out tonight, what do you say? Sometimes it also mean, ¨Do you want to?¨

I hope that was what you were asking. :)