Vqmod is required
With this module you will auto post product on facebook page after you add product in admin
You need to provide app id and app secret.
How to create facebook app is described here http://demo.plusmotiv.com/store/documentation/documentation.html#api
Edit description, message and title or take them from url
It has also add for Multimerch ( when add product from front will post on fb page )
If you want to post old products check this extension https://www.opencart.com/index.php?route=marketplace/extension/info&extension_id=31334