First things first, you need a Provisional License.
When: Earliest - 2 months before your 17th birthday
Price: £34 online (correct as of 09/10/2017)
Time scale: approx 2 weeks to come through
KEEP IT SAFE - you need it!
Studying for the Theory Test can be done as early as you like.
Some essential reading:
The latest Highway Code, find it in most supermarkets or WHSmith, £2.99 approx.
The Official DSA Guide To Driving - The Essential Skills book, £12 approx.
Driving Test Success CD - great for mock tests and Hazard Perception videos, £5-10 approx, look on Amazon, ebay, etc.