Are you trying to use these in a specific context?
Provided that is the one that's more often used as a conjunction.It means that one thing happening is dependent on another thing happening.
I will come visit you provided that my car gets new tires.
Provided that this project succeeds, I will get a promotion.
Sometimes people drop the that and only use provided and it means the same thing.
Mark will come to the wedding provided Alice is not there.
Providing is usually a form of the verb to provide and means to supply/give.
He is providing the food.
I don't know if providing that is used a conjunction. Maybe some places? It's not in American English as far as I know.