Course Enrollment
Before a learner can access your course, they must first be authenticated on the site and that is the responsibility of the site administrator.
There are several enrolmentenrollment methods available to a teacher, what is available, again, depends on the site administrator. The admin might enroll students into the course automatically, or the teacher might be able to let students enrolenroll themselves. This is the Manualmanual enrolmentenrollment method. Other options can be seen in the Enrolment methods link and include Self-enrolment and Guestguest access.access.
An enrollment key may be set if Self-self-enrolment is enabled so only students with the key can enter. The screencast Giving learners course access gives more information on course enrolment.enrollment.