Do you want your Moodle course to be available by big number of students? Once you have actually prepared your Moodle course, you need to provide the access to trainees. You can enroll the trainees in your Moodle course manually one by one however it is a tedious and time taking job especially when you need to enlist numerous users. If you have a couple of trainees to enlist, then you can use Manual registration approach.

Moodle for newbies-- Ways to enable self registration in your Moodle course