@Rachael
I would not consider "words" like wanna, gonna, and kinda to be slang. Is there a category of English called trash?
I will never write "wanna" to my close friend. :)
Wanna is slang and is only used between close friends. Instead use "want to"
I hope that this helps you.
It's the same... The difference is when we use wanna, we don't use "to" for example:
I want to dance > I wanna dance