We've configured Moodle to handle courses and user enrollment differently than Blackboard.
Briefly, courses within Moodle are created automatically from registrar's office records starting six months before the semester begins. Instructors and students are enrolled in these courses automatically when they log into Moodle. Read on for more details.
Enrollment in Moodle is triggered by user login. When a user logs in, the system verifies that user has a Moodle profile and creates one if they don't. The system then makes sure the user is enrolled in the right courses.
Because all this happens at login it's important that students log in to Moodle each semester. If a student doesn't log in at least once each semester, they won't be enrolled in courses in Moodle. But students only need to log in once to be enrolled in all courses they're registered for. The same is true for faculty.
Moodle courses will be available to faculty six months before the relevant semester's start date; students will be able to access their courses two weeks before the semester. Both faculty and students will have access to their courses for two years after the semester ends.
(This post has been edited to reflect changes in the length of time courses are available after the semester's end date.)