To create facebook App ID follow these steps
1. Open developers Web site (https://developers.facebook.com/).
2. Register as a Developer.
3. Goto My App section
4. Create New App.
5. Give some basic details about your Web Site.
6. Then dashboard will open.
7. Goto Settings section below dashboard.
8. Just click Add Platform and then choose Web Site option.
9. Fill up the required fields by entering your Web Site name.
10. Again goto Dashboard section.
11. And click show button to view the App ID and App Secret.
12. Copy those information from dashboard.
13. Fill up the App ID and App Secret in Admin Settings, the place provided in the admin panel of your Web Site.
14. Now you can Sign up and Login into your Web Site with facebook accounts.