There are three default lists (Saved Courses, Taking right now, and Completed/audited) on Class Central. Courses saved using the Bookmark icon go into your Saved Courses list. You can use the Progress icon and dropdown to add courses to the Taking right now and Completed/audited lists on your Transcript page.
Adding a course to any Class Central list does not enroll you in the course. To enroll, see How do I enroll / register for a course?
If your profile is Private, only you can see your profile and default lists. If you have a Public profile, anyone can view them. See the FAQ Is my Class Central profile public or private?
You can also create and name up to 25 custom lists that you can choose to be private, unlisted, or public. You can also add a description of each list (optional). More information about custom lists can be found here.