Facebook page IDs are useful as occasionally a page will be renamed, or a new page will be created under the name of a page that was previously deleted (or renamed). The ID is a way to ensure you have the right page.
To find a page ID you first need the address of the page. This can be seen in the address bar when visiting the page. OHPI’s Facebook page address (for example) is http://www.facebook.com/onlinehate.
To find the page ID simply change the www (or whatever else appears before the “facebook.com”) to “graph”. This gives http://graph.facebook.com/onlinehate. When you press enter you will get a page that looks like this (click to enlarge):
Part of this contains the ID, i.e.:
From this we can see that OHPI’s page ID is 284088808335015.
Once you have a page ID you can visit the page by going to www.facebook.com/<page id>.
Trouble shooting
Note: When using the Graph operation you may occasionally get the following instead:
This indicates that the page in question has either been deleted from Facebook, or access from your country to that page has been blocked. If you change graph back to www you will see this message:
The best thing to do in this case is to ask someone in another country to check the address for you. Ideally someone in the United States as that will be the last place from content will be blocked. If they can see the page, or explain how they can get the ID for you.