wanna = want to
I want to be there at 6.
I wanna be there at 6.
He wants to be there at 6.
wanna = want to
I want to be there at 6.
I wanna be there at 6.
He wants to be there at 6.
explain 1:
It's not exactly politeness, but it establishes a distance, which is an aspect of politeness.
It's a little like a subjunctive.
It shows that you do not assume that the other person will help you.
It's like the difference between: