There is no admin output for this module

Yes, that is correct. Website builder module does not have output in admin area; therefore, built-in WHMCS message "There is no admin output for this module" is displayed.

The module only adds button "Open Site Builder" (or "Open [your-builder-name]") in client area to each product details page of hosting type. Please log in to some WHMCS client, open details of some hosting service and you will see this button in the right side menu box.