* The vehicle title
* Proof of insurance
* A valid driver's license
* The vehicle registration fee
* A smog inspection certificate (if applicable)
In some states, you may also need to provide proof of sales tax or a lien release.
If you are financing the car, you may also need to provide a copy of the loan agreement.
Once you have all of the required documents and items, you can take them to the DMV to register the car. The DMV will then issue you a license plate and a registration sticker.
If you are not able to register the car when you first buy it, you will need to do so as soon as possible. Driving an unregistered car is illegal and you could be ticketed or fined.