To get you started with driving you must first apply for a provisional driving licence, you can apply for your first licence online at the following web address http://direct.gov.uk/en/Motoring/Motoringtransactions/BeforeyouapplyA/DG_10032690 You can also pick up a D1 Application form from you local Post office and fill in the form and provide one form of identification, provide your address over the last three years, a passport style colour photograph and a fee of £50.
Normally, for car drivers, the earliest date your provisional license can become valid is on your 17th birthday, however you can apply for the licence up to three months before your 17th birthday. So, if you apply for your provisional licence before you are 17 you will still have to wait until your birthday before you can take your theory test.
You can apply for your theory test as soon as you have a provisional licence. The price of the theory test is £31, the theory test covers two parts, multiple choice (50 questions in which you need 43 to pass) and hazard perception (75 points in which you need 44 to pass). More details on theory test can be found on the following link http://www.direct.gov.uk/en/Motoring/LearnerAndNewDrivers/TheoryTest/index.htm
Once you feel you are ready to go for the test you can book your test online on the following link http://www.direct.gov.uk/en/Diol1/DoItOnline/Doitonlinemotoring/DG_197299
You will need you provisional licence and your theory test certificate number to book a test. The price of the practical test is £62, however weekends and weekday evenings bookings are £75. To change or cancel a test you will need to provide three clear working days and follow this link http://www.direct.gov.uk/en/Diol1/DoItOnline/Doitonlinemotoring/DG_197300