Static Web Hosting: Add a Domain such as https://example.com

On the Web tab in https:/box.example.com/admin page, it says

To add a domain to this table, create a dummy mail user or alias on the domain first and see the setup guide for adding nameserver records to the new domain at your registrar (but not glue records).

Can someone please explain the steps in full? I have added a user for me@example.com but the domain, example.com, still does not show up in the table in Step 5.

Thanks,