Basics on Moodle course creation & course rosters:
Course shells are created for your courses about a week after the registration period for the upcoming semester -- roughly late November and late April. They are created as hidden from students so that you can organize your materials as you want them before allowing students to view.
The rosters for your courses are created and updated automatically by a data feed from MyMountHolyoke which runs several times per day. In most cases, you will not need to do anything to maintain your rosters in your Moodle courses, but you do have control to make changes and allow access as described below:
Guest access (non-MHC or Five College)