The word "wuz" that you have written is not correct, and does not exist. The correct way to write it is "what's up?" (contraction) or "what is up?" It is a slang greeting used mainly in the US. You may be aware of a very popular smartphone app called "Watsapp". This is a wordplay. It combines the word "app" with the expression "what's up?" Meaning: In the US, it is used in a way that it implies "what are you doing?" or "what is new in your life?" or "what's your latest news?" or "what is going on?" However, in the UK, it means "what is the matter? Why are you sad / upset?"

"Wuz up" could be used in the UK to mean how are you, very informally and also ironically, perhaps referring to this funny old advert from the USA: https://www.youtube.com/watch?v=tauYnVE6ykU "What's up?" could also be said in a concerned tone to mean "what's wrong?" (in the UK)

Adding to what Elena said, this would be used in informal situations such as when you are talking with friends or, maybe, family. You wouldn't want to use in business settings or with teachers.

Yes, it's short form for "what is up?" - informal way to say "how're you?" and "How're you doing?" (as a rule, in US)