A brief summary of how to get your licence:-
If you are 16 years of age you must apply for a provisional motorcycle licence. Once you have completed a CBT, you can ride a motorcycle or scooter up to 50cc - unaccompanied with L plates. You cannot use motorways or carry a passenger.
If you are 17 or over you must apply for a provisional motorcycle licence. Once you have completed a CBT, you can ride a motorcycle or scooter up to 125cc and a maximum of 14.6hp - unaccompanied with L plates. You cannot use motorways or carry a passenger. The CBT has a 2 year lifespan if you do not take and pass the full motorcycle theory and practical test.
If you are 17 or over you can train for and pass a restricted motorcycle test on a 125cc bike. This enables you to ride any size bike that is restricted to 33hp for a 2 year qualifying period. After this you can ride any motorcycle without restriction.
If you are 21 or over you can train for and pass the full motorcycle test on a large motorcycle (more than 46hp). This allows you to ride a motorcycle of any size that is unrestricted. This is called Direct Access.
The theory test must be passed before the practical motorcycle test can be booked.