It’s not grammatically correct. It should be, have you been up to much? It means, what have you been doing?

It is a friendly but slang way to say "What have you been doing recently? It is a different way to say "What's new?" to your friends. It is informal.

''(Have) you been up to much?'' = ''Have you been doing much?'' We tend to drop the ''have'' at the start of the sentence in spoken English. I wouldn't go so far as to say that it's ''slang'', it's just informal. I'm sure I would write it like this myself in, for example, a text message.

Means earn lots of things in life..

It means have you been doing a lot of things recently? It isn't strictly incorrect in a way, people talk like this when texting, it's text language.