In case you already have a Facebook App and want it to use "manage_pages" and "publish_pages" permissions you will learn how to enable them in this article.
These permissions are needed for Facebook App to be able to publish posts on your Facebook Page. Once it is in the developer mode you can make any publications on the Facebook page through the Facebook App without these permissions.
However, being published while in the developer mode posts aren't seen to anyone except for the page administrators and Facebook App developers. That is because Facebook needs to confirm the manage_pages and publish_pages requests, to make them seen to the public.
In order to request "manage_pages"