Clicking students you will find the note saying that students themselves can enrol to your course as soon as they know the enrolment key, which is also reminded here. That means that giving them the enrolment key might spare you ever checking on that page. Still, you can enrol/unenroll students manually without giving them the enrolment key.
Below, you will see two fields separated by two arrows (left/right). The left field lists enrolled students to your course and the right one contains the names of all potential students (i.e. students that the system already has registered). To add a student to the course, find their name in the field on the right, highlight it and click on the left-facing arrow, which will transfer the student to the left field (you can also type in the student’s name in the “Search” field if there are too many students to list).
To unenrol a student from your course, you should repeat the above procedure but this time transferring the student from the left field to the right one (using the right-facing arrow). The student should move from the “Enrolled students” column to the “Potential students” column.
If the course is a meta course then the page changes from listing/searching for students, to listing/searching for courses.