There are different ways to let your users create a new account:

Both the form and portal allow you to have a login page. Which could also enable new signups. Go to:

This option allows users to create new profiles to sign up if they don't exist already.

You can add a link for the user registration form to the portal's login page. You can set this up in Login Page Subtitle. Here's an example:

You can also email users a link that takes them directly to the registration form. You would need to set up one first.

The login info is not stored in the extension itself. They are records in Airtable. The login fields would be columns in your users' table.