From a private seller, you can't. You would have to
buy the vehicle, ad it to your insurance policy, then
get the title from the seller. Take the title and proof
of insurance to your local motor vehicle agency.
Transfer the title to your name, register the vehicle
and get new license plates. Then take the new
license plates, registration, and insurance card with
you to pick up the vehicle. Now if you were buying
from a Dealer, you would just need proof of
insurance and the Dealer would issue you a
temporary license plate to drive the vehicle home.
Hope that helps! Jim