Correct Responses Options

[xTINAA]

(I'm not sure if there are topics like this, if so, oops)

You know those questions that don't exactly seem to have a clear cut response? How are you and how do you respond?

I have an example. The question, "What's up?" The typical answer is, "Nothing." I was on the phone with a friend and he asked me that and I said, "I'm just driving, you?" and he says, "I didn't ask what you were doing, I asked what's up." But isn't that basically the same thing or am I a complete idiot? He then continued to ask me again, I gave him the typical answer, and then he asked me what I was doing. Doesn't that seem redundant? What's the point of asking if you're expecting to hear "nothing"?

So, how do you respond to "What's up?" or "What's good?" or any other questions that have somewhat unclear responses?

Sorry if this makes no sense haha (: