Step1: Go to facebook developer site and login. Here is facebook developer link https://developers.facebook.com/apps open this and login to developer account.
Step2: Click on “My App” tab and select “create new app”.
Step3: Choose your platform “Android”
Step4: Enter your App name and click on “Create New Facebook App ID”.
Step5: Choose your category and click on “Create App ID”.
Step6: Enter your package name and your default Activity class name.
Step6: If your app already published on Google Play Store than it will find otherwise ignore this message and click on “Use this package name”.
Step7: Add your development hash key and release hash key.
Step8: Creating new app is finished
Step9: Click on “Skip Quick Start”
Step10: Here is your app id