A group is a collection of students in a course. Outside of a course, a group has no meaning.
Groups are useful when you want to separate students studying the same course. For example, if your organization is using the same course for several different classes or groups, you can use the group feature to separate students so that each group can see only their peers in the course.
You may want an activity or resource to be open to just one group of people. You don't want others in the class to be able to use that activity or resource.
You can apply the groups setting to an entire course. If you do this, every activity and resource in the course will be segregated into groups.
You can also apply the groups setting to an individual activity or resource. If you do this, it will override the groups setting for the course. Also, it will segregate just this activity, or resource between groups.
For a course or activity, there are several ways to apply groups.
No groups: There are no groups for a course or activity. If students have been placed in groups, ignore it. Also, give everyone the same access to the course or activity.
Separate groups: If students have been placed in groups, allow them to see other students and only the work of other students from their own group. Students and work from other groups are invisible.
Visible groups: If students have been placed in groups, allow them to see other students and the work of other students from all groups. However, the work from other groups is read only.