COPE3:Hi. I've just bought a used car and would like to know what to do afterwards. I know I will have to buy insurance, but what else do I need to do, and how do I do it. I am guessing I have to go to the post office to fill out some forms, and pay money, but I am not completely sure. Thanks.
You should have been given the V5 registration document if private purchase to send to DVLA with your details. If you bought it from a dealer, they will send it to the DVLA on your behalf and you will get it back within a week or so.
See DVLA guide http://www.direct.gov.uk/en/Motoring/BuyingAndSellingAVehicle/index.htm
Why would you be going to the post office and paying any money. It there no road tax?
If bought from a garage and there is a warranty, check the car throughly and get any faults that may be covered fixed by the garage.
Huckster