The edition page of an override is pretty much the same as any other email, but with one main difference: the "{paramx}" elements in the subject and content:

In the default email that should have been sent by your website, there are some dynamic information such as the user name, the site's name, the confirmation link, etc...

You can insert this information when editing a text zone by clicking the "Dynamic text" button:

In this email for example, you will be able to insert the site name, the username and the email address of the user, because this information will be gathered from the original email by AcyMailing.