It's an informal style of writing, "wanna" is actually "want to". You will find this type of writing in comics and such, but this spelling is not acceptable in formal contexts.

You normally use "wanna" in a casual setting. The meaning of "wanna" is the same as "want to". I will give you some examples to help you understand. - I wanna drink coffee. = I want to drink coffee. - Do you wanna go to the park? = Do you want to go to the park? - What do you wanna get? = What do you want to get? However, you can't use it as a replacement for "want". - I wanna water ≠ I want water. I hope this helps.

I think wanna is more colloquial.want to maybe always use in formal situation.