SECOND HAND CARS: I assume that you have had the car checked etc and you are sure it's the one you want to buy? You've paid the money & got a receipt? OK, first you have to get a permission letter from your sponsor and then take it to one of the special police stations usually with the seller of the car, but I have heard of doing it just with his/her ID card, where you fill in a special transfer form (you can get this done for QR10 one of the typing booths outside...if you are foreign they will try to charge you more) wait in a queue to see a clerk (while he deals with all his mates who are buying number plates) give him your ID card + the ID card of the seller + the sponsor letter + the form + the ID card for the car + (maybe) the insurance certificate (take it just to be sure), wait while he updates the computer & makes a new owner's card for the car, pay him QR200 with credit/debit card. That's it!
Finally you have to transfer the insurance to your name-sometimes the existing owner does this, sometimes not. If not I got a permission letter from him, again just in case.