From GroupScript documentation
Facebook Connect is disabled by default. It can be enabled in Backend->Settings - Facebook options.
You need to set up an application at Facebook and configure the domain name and site URL in Application config at Facebook: http://developers.facebook.com/setup/
Previously, Facebook API details (application id and secret key) had to be stored in system/application/config/fbconfig.php. Since version 3.0 this is done in Backend->Settings - Facebook options.