You can set your social media URLs here. You can manage share buttons on pages here as well. The share buttons option can be enabled/disabled for each and every post type.
You can enable Facebook comments, in this case WordPress will use Facebook Comments instead of WordPress default comments system.
If you would like to use the Facebook comment ability it recommended to set a Facebook App ID which belongs to you to be able to moderate the comments.
If you are using any Facebook related functionality (Facebook Shop Tab, Facebook comments, etc.) you can enqueue the Facebook SDK. If you are using a plugin which already enqueued the SDK you can disable this option.