Before you drive off the lot, be sure to have a copy of the contract and all other documents that you and the dealer have signed. The credit price is shown below as the "Total Sales Price.When you buy a car at the dealership, you'll need to sign the car purchase or sale agreement along with other documents. Find out what you'll sign and why. Complete the paperwork. If working with a dealership, they will handle much of this process. The final hurdle you face is signing the vehicle purchase agreement; a confusing and convoluted document that we explain in detail here.