Before you start to generate Facebook App id. Take a look on facebook development.
Facebook allows you to obtain a token to access Facebook’s API on behalf of someone using your app. You can use this feature in place of building your own account system or to add Facebook services to your existing accounts.The Facebook SDK for Android provides methods to implement Facebook Login for your app. And to access this feature into your app you need facebook app id.
Now start to generate facebbok id , you should need a facebook account as a developer or you can use your personal account also. Step1: Goto facebook developer site and login.
Here is facebook developer link
open this and login to developer account.