Ok.
You need a transfer letter. Available at Civic centre, Karachi.
The transfer letter ensures that the car you own now comes in the ownership of the buyer once the payment is done.
Payment recipt ... for assurance that you have been paid the amount by cash/cheque and have signatures and ID copies of both parties.
Delivery letter. Its a letter which gives the time and date of delivery to the new owner. This assures that any problem in or related the car after the delivery is the sole responsibility of the new owner.
Bayana letter is something like the buyer pays you a bit of the amount so that if he backs out after assuring you he is buying your car ... you keep the money. This is to prevent the buyer to back out since you might get a better deal during the time he says he wil lbuy the car. And also you cant back out of the deal. Confirm this part by someone else as the last car I sold I didnt take bayana because the person was an co-worker at dads office.
All original ownership papers of the car and tax recipt is to be given to the new owner. Also the new owner might call CPLC to verify that your car is legal.