If you are looking to simply limit the number of people that can complete a registration form, you are in the wrong spot - here is the article you will need:
In addition to setting a limit on the number of people that can register through a form, you can also set limits on additional items within the registration form. This could include an additional camp, ordering specific items with limited quantities, or registering for a limited number of spots volunteering.
To set additional limits with waitlists in a registration form:
1. Go to Registrations
2. Create a new form or edit an existing one
3. Go to the Additional Info tab
4. Click Add New Custom Field
5. Select either Dropdown (Single Selection) or Dropdown (Multiple Selection)
6. Enter the Max Selections and whether you want to offer a Waitlist or not. Once you're done, click Save