Fidoi's right - "wanna" means "want to". It can also mean "want a".

If you want to sound native in your writing, DON'T USE IT. English learners typically write "wanna" and think that they sound more native, but it's really the opposite. In regular, everyday English, native speakers use "want to".

Same with "plz" (Use "please", please).  If you want to use English at native-speaker level, just use the regular forms.

"Wanna" is an informal way of saying "want to".

It wouldn't be appropriate to use it in a formal situation. However, you could use it when texting a friend, for example. 

You wouldn't use 'wanna' in writing or if delivering a speech on a podium, but that's about it with the restrictions... even in formal situations, it is used in speech I've found eg in business meetings or dealings with government departments etc (both on phone and in person).