To allow users to enroll in courses, we will enable the corresponding enrollment option.

Go to Admin Panel > Courses > Courses and find the course where self-enrollment will be activated. For this course, open the context menu and click Edit. Under Enrollment Options, select Self-Enrollment. If you want, you can even set a date range during which self-enrollment is active, as well as an enrollment code required to enroll in the course. Save to finish.

Once the course is configured, you can send the course link to any user, and when they click the link, they will be redirected to the self-enrollment page, where they can enroll in the course.