What is the co-relation between Custom Metadata, Metadata Group and Metadata Set?

In eMAM, custom metadata can be organized into Metadata groups and Metadata sets.

For a user, the metadata fields displayed will be based on user permissions and asset type (audio, video, image, and other files such as documents). 
Custom metadata fields can be organized into Metadata groups. Each user group can be assigned different permissions to restrict the Update and View permissions for the metadata fields inside the group. The Metadata groups can be assigned to different user groups which would control permissions for users in those groups. In the Admin Tools page, under Manage User Groups, administrators and authorized users can associate user groups with metadata groups.

The Metadata groups, in turn can be organized into different Metadata sets. A metadata set contains metadata groups, which contain metadata fields.  Each metadata set can be assigned to an Asset or a Project or a Category or Marker or Subclip.