After you have set up a waitlist for your event, when a ticket type has sold out or the event capacity has been reached, a link to access the waitlist will appear on your event page.

Potential attendees will be able to add themselves to the waitlist by entering their information and they will receive an email confirmation of their placement on the waitlist.

To manage your waitlist and release tickets, click on the title of your event from the My Events page and then select "Manage Waitlist" from the left-hand feature menu.

Here, you can view the list of potential attendees who signed up for the waitlist and you can release tickets to those people at any time.  You can also manually add people to the waitlist from here.  

When you do release tickets for the event, the potential attendee will receive an email notification with a link to buy tickets/register for your event.