There are two different requirements - one is for an Operators Certificate, in this case a Short Range Certificate, which is issued following successful completion of a course which teaches and tests the operator's competence in using the radio's functions, including DSC, along with the correct protocols and terminology when communicating.
This is a legal requirement in order to transmit on a marine VHF radio other than in an emergency situation.
Separate from this is a requirement to license the radio itself, in most cases here for a hand-held radio, so it would be a Ship Portable Radio licence - this registration is required for an MMSI number to be allocated to the handset which then enables the DSC capabilities. This is free of cost if done online and importantly no proof of an Operator's Certificate is required.
As has been mentioned, earlier posts on this thread give more detail and links.
