You can choose which roles will be available in your group.
Course groups contain tutors as well as administrators and ordinary members. If the group allows members to submit pages to the group for assessment, tutors and administrators can assess those submitted pages and provide feedback in the form of comments to the authors.
Outcomes group have administrators, tutors, and ordinary group members. Portfolio collections are automatically set to be outcome collections, but a different type of portfolio can be set up. Outcomes groups allow everyone to edit portfolios, but only administrators can set up outcomes collections and outcomes. Tutors can set up activity pages within such collections and can add supporting comments. Ordinary group members can add content to activity pages, but not sign them off.
Standard groups contain administrators and ordinary members. Administrators manage the group, its membership and permission options. Ordinary members cannot edit the group settings and membership, but they can usually post in the forums as well as edit pages and files belonging to the group.