"What's up" is a short quick way of asking "What's going on in your life right now? Or "What is going on?" It is similar to but not the same as "How are you doing?" It is a hard, awkward question to answer even if you are fluent in English! You could say...."Not much" or tell them WHAT you are doing at the moment. But don't tell them a long story!!!

The question "What's up?" has almost the same meaning as "你怎嘛样？" It's meant as a "small-talk" way to greet other people. A typical answer is "not much." Sometimes, because the question itself is not as important as the desire to communicate, people will sometimes say "Good!" (even though it's not a correct response to the question. The meaning of "what's up?" (or "What's new?" or "What's happening?") is 最近，您在做什么，您的生活如何？ In Chinese, if someone asks "你怎嘛样？" a typical answer is "不错." In English, is someone asks me, "How's it going?" I will often answer "Good!" (even if things aren't perfect).

Yo!

You can reply just as you would when someone asks you, "How are you?"

‘What’s up’ is short for ‘What is up (with you right now).’ It’s like asking how you are going. You can just respond with how you are feeling, talk about something that has happened to you recently, or simply reply with ‘It’s all good e.t.c.’