You can enable Facebook comments in Theme Options > Social Media. If you enable this feature 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. You can also set Facebook Profile IDs for moderation, but not both.
You can set the Number of posts, and the order of posts. You can order the post by: Time, Reverse Time or Social (by posts popularity). These settings can be overwritten in Facebook Comments shortcode.
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.