Hi Gary and Julius,
Maybe there's a vocabulary problem between what Moodle calls a "course" and what is called a "course" by students and teachers outside Moodle.
In Moodle, a "Course" is an area in which a "Teacher" can insert, in a logical order, a number of "Resources" and "Activities".
If there are no "Groups" or "Groupings" all the "Teachers" and "Students" in a course area can "see" each other.
If the teacher sets up "Groups" and "Groupings," sets of "Students" and "Teachers" can be totally isolated from each other: they are all using the same "Resources" and "Activities" but not aware of the presence of people in the other "Groups/Goupings". From the the student's point of view the course is their "Group/Grouping" - they don't need to know these words - for them, they're just in Course c10a or Course c10b, each with their respective teacher (who can be the same or different in each Group/Grouping).
To be honest, it took me a little while to get my head around the idea of Moodle "Groups" and "Grouping" and to work out how to set them up but there are the Moodle Docs and video tutorials too. For example:
Cheers,
Glenys