You pay the tax at the county tax office upon registering the vehicle. See link below for information.
http://motor.etax.dor.ga.gov/motor/registration/regrequirements.asp
Be careful! As long as the car is titled to a private owner, NO you don't have to pay sales tax. But we made a huge mistake! Thought we were buying from a private individual but he put the title in...
You have to get insurance on that car and go to any County tag office in GA for a new title or registration and a new tag.
Certain year model cars require you have the title - not just a bill of...