A mentor is the person who you can talk to about your educational needs. This person may help you to choose the place where you work to gain most experience, choose your special topics and answer any of your questions about the Diploma.
A supervisor is the person in the clinic where you do your core training (Gynae, Family Planning or Sexual Health) who allocates your work times and to whom you are responsible for your clinical work.
A tutor is the person who teaches you in the form of case discussions and any particular questions you need answering on a regular basis every week or fortnight.
The tutor and supervisor may be the same person in some areas, but may be different people.