First of all you need to obtain a provisional licence. Then you need to take CBT training and pass that test. That validates your provisional licence for 2 years and you can go on the road with L plates on a moped or learner motorcycle.
(A moped has a maximum design speed not exceeding 50 km/h (approx. 31 mph). It has an engine capacity no greater than 50 cc and can be moved by pedals, if first used before 1 August 1977. A learner motorcycle has an engine up to 125 cc and a power output not exceeding 11 kW.)
Then you go on to train for and pass your theory and practical driving tests.
There are two types of full motorcycle licence, depending on what you took your test on. :
A light motorcycle licence (A1), which restricts riders to any bike up to 125 cc and a power output of 11 kW. The practical test must be taken on a bike of between 75 cc and 125 cc
A standard motorcycle licence (A), is obtained if the practical test is taken on a bike of over 120 cc but not more than 125 cc and capable of at least 100 km/h per hour. After passing the standard motorcycle practical test, you will be restricted for two years to riding a bike of up to 25 kW and a power/weight ratio not exceeding 0.16 kW/kg. After this you may ride any size of bike.
There are additional options for those over 21, but they won't apply for you at the moment.
For what it's worth, 11kw is 14.6bhp, 25kw is 33bhp.
And I'd press home a tip of being very careful to keep your CBT certificate, and for that matter the paper copy of your licence. So many are about to go for their tests and realise too late they've lost them! Keep a photocopy for reference purposes.