When you buy a used car from a dealership the used car dealership should be able to issue you a temporary paper license plate that will allow you time to get to the DMV to get the vehicle registered and have a regular license plate registered to the vehicle.
After buying a used car from a dealership or private part you usually have 2 to 3 weeks to get the vehicle registered and have a regular license plate issued.
Be sure to keep the paperwork in the car if you just bought it and are driving without license plates in case you get stopped.
In most states you can usually drive the vehicle from the place of purchase to your home or where you're gonna store it and then you'll need to get the license plates for the vehicle before you can drive it any further.