At Admin -> Settings -> Social, you have an option to enable a facebook app. If you turn this on, two new templates will appear at Admin Panel -> Themes -> Manage Templates: "Facebook App Wrapper" and "Facebook App Front Page". These templates will control the appearance of a facebook app edition of your WSN site.

You will also need to go to https://developers.facebook.com/apps to register and configure the app with facebook. Use any app name and namespace you like. Type in http://yourwsninstallationlocation/facebook.php?dynamic as the Canvas URL (replace yourwsninstallationlocation with your actual site URL). Keep it as an iframe. For the privacy policy, use http://yourwsninstallationlocation/facebook.php?action=privacy

By entering the app id and secret on the social settings page you can enable facebook connect logins as well.