This feature adds a Facebook share button to the list of banners in the affiliate panel so the affiliates can easily share their banner links.
You can activate this feature as any other from your merchant panel Configuration -> Features where you click "Activate" next to the "Facebook connect" feature.
Once the feature is active you can see the Configure button next to it which lets you define ID of your Facebook app. If you do not create a Facebook app the share button will only share your affiliate's link without pushing through also the banner image, however you might be able to add some API coding to your website so it will trick Facebook into fetching the actual image of the banner instead of an image directly from your website. This approach is described in the second point of the Facebook Connect FAQ article.
Alternative approach is to create new Facebook app from https://developers.facebook.com/, however you first need to have a developer account there. You can log in with your regular Facebook login and then click on "Get Started" in the upper right corner and go through the verification process. Once verified, you'll be able to name your first app and create it. If you already have a developer account you can create a new app via upper right corner My Apps section and the Add New App button.
Once the app is created do not add any "Product" to it and instead go to Settings->Basic on the left side menu. Scroll down and click on Add Platform and select Website. Once added add your Post Affiliate Pro domain or the custom domain (if you have set one up) as the Site URL. You must add the domain which your affiliates will use to log in to their affiliate panel. Afterwards still on the Settings->Basic sections scroll up and add your domain also to App Domains. Save the app and take its ID from the top of the site. Put the ID into the configuration of the Facebook Connect feature in your merchant panel.
Once this is set up your affiliates can easily share image banners including the image of the banner.
NOTE: Impressions of banners shared on facebook can not be tracked due to technical limitations.