When a Program is full (reached Enrollment Maximum - see Program Fields), you can Add prospective registrants to a Wait List by going to that Program and clicking on the Wait List tab. Click the Add to Wait List button, type in the first few characters of the member's Last Name and choose them from the drop down list. Member's will be added to the list in the order they're entered.
If a spot then opens up, you can initiate a Registration from the Wait List by clicking on the Register button and following the workflow at Registering people for programs. Once the registration has been processed by going through the checkout process it will automatically be removed from the Wait List.