Getting Started with Register Plus Redux

I am with andywt. I can see the settings page but when I use the “Preview Registration Page” button it opens ../wp-login.php?registration=disabled and gives me an error.

From what I could figure out from other posts I should add the “short code” to a page to get access to the customised registration/login screen. Problem is I am new to all this and don’t know what the short code is or where to find it.