Wallflux helps you to find the Facebook ID of Facebook groups. A Facebook ID is a many-digit number, eg.
Besides for groups, the service might also find the ID for other Facebook entities such as pages, users, apps, but dont be upset if it doesn't. Also, no use trying twice: if the service can't find it the first time, it won't be able to help you.
If you're really lost, you can contact
Wallflux for your Group ID.
Paste a complete Facebook URL - for example
This page will then try to come up with the Facebook ID and its associated Wallflux feed.