You will need a provisional driver's licence, this can be applied for using form D1 available from Post Offices. More information can be found on form D100 or at the DVSA web site. See links page.
Once you have got your provisional licence and turned seventeen you can start your driving lessons.
You will also need to study for the theory and hazard perception tests. I can supply study guides.
The number of practical lessons required depends on how quickly you pick up the skills required to become a safe, independent driver able to cope on your own on today's busy roads.
See the DVSA web site for recommended practical hours.
Some useful publications to help you study are..
The official DVSA guide to driving "Driving The Essential Skills"
The Highway Code
CD's and study aids for the theory and hazard perception tests are all available from The Stationery Office, see the links page for their details.