A fast, powerful car will doubtless be expensive to buy, and will also be costly to insure. A performance car isn't a great idea for an inexperienced driver, your speed is likely to 'creep up' in a powerful car, making it easier for you to lose control. Consider buying a smaller car – the car will be cheaper, the controls are lighter, parking is easier and insurance is cheaper.
First, figure out your budget. You should include the cost of insurance, road tax, and any extra for any necessary mechanical work. Then do your homework and research reviews to decide on the right make for you. If you're buying a new car go to a recognised dealer. If you want a used car, try franchised dealers for the best after-sales support. Independent dealers are good for slightly cheaper cars, and classifieds and the Internet for private sales which are cheaper still, but your legal rights are limited.
Ask about its service history and check the car's documentation, including vehicle registration certificate (V5C), which shows the registered keeper of a car; MOT certificates (make sure they are annual if the car is more than three years old); and paperwork showing its full service history. Be aware that an MOT certificate doesn't mean a car is roadworthy or safe. It means it passed the MOT test on the date the test was done.
An AA Car Data Check can ensure that the car you're considering has the correct documentation and has no outstanding loans against it. The report will also inform you if the car has previously been involved in an accident and the insurers have written it off, or if the car shouldn't be on the road and you wouldn't be able to get insurance to drive it. See details of what's covered by an AA Car Data Check.
Absolutely. And make sure you drive it for at least 30 minutes. The aim is to see if you like the feel of the car and if the steering and brakes work properly. If you're unsure about the car in any way then get it checked out by an expert (see AA Vehicle Inspections). Don't be pressurised into buying on the spot, and don't be afraid to haggle (all dealers expect this).
Also check out more detailed advice about choosing your first car.