Training Sessions are made by Content Creator account types Admin/Project Owner. Once a Training Session is created, Admin/Project Owners can invite user accounts as Participants to Training Sessions as either a Trainee or a Supervisor.
Importantly, any account type: User, Admin or Project Owner can be made into a Trainee/Supervisor in any given session.

In short: Trainees can engage with Training Sessions & content within them if they have been invited.
Supervisors can do the same, and additionally can manage themselves and other trainees within the session and view scores.

* = if annotations creation/review are activated in the current interaction mode