If you have never been on a public road before, we would strongly advise practicing the motorcycle theory test or the Ride Free pre CBT course to gain extra help with the Highway Code/road safety information.
If you have not taken a full licence in the following two years, then you have to repeat the C.B.T. course to continue riding as a learner. At age16 you can only ride a 50cc moped, at 17+ you can ride a 125cc.
Talk to your local training school about any of the above steps. If you have any concerns they will be able to answer them for you. If you're wanting to ride a bike larger than 125cc, then this would involve first passing the motorcycle theory test (just the same as you would before taking a full car licence)
Your training school will best advise you of the amount of training that you require as an individual before taking the full motorcycle licence. This is usually done at the end of a satisfactory CBT road ride.