This 'Deploy' button will allow you to use your App ID and App Secret from your Facebook App dashboard to host your own Facebook app.
You need a Heroku account which is free, and offers many useful tools for computer science students :)
Once you click the button, and after you login/make your account, you can enter your App ID and App Secret into the provided boxes on the bottom of the page.
Once you gave your application a name, and entered your App ID and App Secret, head back to the dashboard of your Facebook App and update your app domain and site url with the following information:
your-app-name-here.herokuapp.com
Then go to Facebook Login settings on the left panel and enter this for the redirect value :
your-app-name-here.herokuapp.com/auth/facebook/callback