You can manually enroll students for a course, see how many students are enrolled, and—if needed—unenroll students using the Instructor Dashboard. Students can enroll themselves as well during that course's enrollment period.
For a course on edx.org, enrollment is publicly available for anyone with an edX account. For other courses, such as those on edge.edx.org, students can enroll themselves using the course URL you provide (it is not available to the general public); you can also directly enroll students.
Before a student can enroll in a course, they must do the following: