Yes, your response is not so different from that of native English speakers. "What's up?" means exactly the same thing as "what's new?", so the correct response is to report whatever new events are going on in your life, or, more often, to answer "not much"--or even to do a combination of both. For example, A: "What's up?'' B: "Not much. I just got home from work." That's a pretty standard type of interaction. To answer with another question is fine, since "What's up?" is only the smallest bit different (a little less formal) than "Hello.''

It means "what are you doing?" "what have you been doing?" and "What is new in your life?" Like the person above said, it is more of a greeting than anything. You can respond with "Hey how are you?" or something as well if you like.

U say its geting alone fine hows your life doing

It isn't a stupid question . It's slang A better way would be to ask " How are you ? " or any other way to catch you attention. Amongs friends it is very common to ask like this.