You must undertake CBT (compulsory basic training) before riding a moped on the road, with training provided by an approved training body. Following successful completion of CBT, you will receive a Certificate of Entitlement (CoE) which allows you to ride a moped on public roads.
To continue riding a moped beyond 2 years after completing CBT, you will need to obtain a full moped licence by either passing the practical moped test or taking a theory test followed by a practical test.