In the UK, we are issued with our plates from the Government Organisation, (the DVLA) several days before delivery. This gives us time to arrange our insurance for the car in advance, and for the car to be taxed and registered by the dealer.

Without a plate, tax, or insurance, the dealer won't let us drive the car away.

I was lucky enough to receive the Owner's handbook in advance, so I could familiarise myself with the features.

Second hand cars have already been registered etc. so you can simply ring your insurance company, pay the premium, wait for the cover note to be faxed to the dealer, then drive away the same day.