First, login to your BigCommerce Store Administration and click Storefront --> Footer scripts.
Now copy and paste your snippet text, which looks like the below, into the box, and click save.
<script src="https://whatthefaq.herokuapp.com/js/widget.js"></script> <script> WTF_Lib.init([" YOUR_API_KEY_HERE "]); WTF_Lib.check(); </script>
.. and you should see a nice green message:
The widget will now display on all the pages you have added here on WhatTheFAQ.