Enrolling in a course or track is simply a way of organizing your work flow. You can enroll in a course individually or in a track. If you enroll in a track you will automatically be enrolled in all the related courses. You can un-enroll from either at any time.
When you enroll in a course or a track they are added to your "My Classroom" page.
Not that courses will only show up as "In Progress" on the "My Classroom" page and in the Progress quick check widget if you have completed at least one lesson in the course.
To learn more about how enrolling works, see this article here.