If you want to safeguard the deal, you need an automobile bill of sale to clearly state the details of the car that you are buying or selling.
If you do want to re-sell the car, your bill of sale from the person you bought it from will instill confidence in the buyer.
They will know that it was not stolen or didn't come from some chop shop.
Register and Insure
You will need a proper form to register and insure the vehicle. Check what you need with your state's DMV.
A bill of sale form for an automobile should mention year, make, model, color, VIN, engine number, odometer reading and the specific details about that, etc.
The form you will print from this file is a very sharp version.