The permissions tab allows administrators to create/edit/delete roles and specify what level of access each role has. The default roles for a new Medici installation are:
In Medici 1.2, the Anonymous role has been added, but has no permissions set. If you want to use this role, then you will need to assign permissions to the role.
You may have noticed a role on this page that does not show up in the Users tab: Owner. The Owner role is not an assignable role; it is a special role to specify ownership of a dataset/collection. If you need to reset roles and permissions do default, you can do this by clicking on the link at the bottom of the page: Set all roles and permissions to default.
Note: This will reset all users to inactive and remove all assigned roles. Only the administrator role/user will be active. It will also delete new roles that were created and are not part of the default Medici roles.