I believe that in a statement, you would use "has" when referring to : he/she/it.
And, you would use "have" when referring to: you/I/they/we.
Eg. He has the ball. She has the ball. It has the ball in it's mouth.
You have the ball. I have the ball. They have the ball. We have the ball.
My question is who do you refer to when you use "has" and "have" when asking a question?
Eg. Do you have the ball? Do they have the ball? Does she have the ball?
Who has the ball?