How to create an object in the FB app ?

As of Graph API v2.8, custom Open Graph action or objects can no longer be created in the application.

You can read the changelog here - developers.facebook.com/docs/graph-api/changelog/version2.8

Custom Open Graph Actions - Apps can no longer create new Open Graph action or object types or publish Open Graph Stories that use custom action or object types. Approximately 1 year after the v2.8 release, no version of the API will allow publishing stories that use custom action or object types. Please see our deprecation guide for more information.

-Melissa