Go to developer.facebook.com and go to products -> messenger platform --> "start building" Click My Apps in top corner & Add App.
After you create your app you will see a list of products. Click Messengers Get Started Button until you see a page with some text fields to fill in. You will need some information from this screen.
Generate a "token" by clicking Page and selecting the page you just created for your bot, for example "DukeBot" if that were such a thing
Copy this token and paste it in on the facebook_bot.js file in place of the "insert your page_token from facebook here" at the very top of the page.