Can anybody explain me what the "whats up" means? Is it "how are you" or " what are u doing"?

Question

Answer

Hey!

Sometimes it doesn't mean anything. Just one of the ways to greet someone: "Hey, what's up?" = "Hey, what is going on?"

You can also ask it when you see that someone is upset for instance. Then "What's up?" would mean "What is up with you? Why are you sad"?

Answer

It's kind of a combination of both. But mostly it means "what are you doing". It all depends on the context.