How do I add scripts?

I’m trying to add the code to this guide; https://github.com/ethanaobrien/emulatorjs
But I can’t do it. I’ve tried everything, including your plugin. I’m sure I’m doing something wrong, being a beginner and no knowledge of JS.

Also, I don’t quite understand where to copy the {{CODEmyjscode}} code after adding the script in preferences.

The page I need help with: [log in to see the link]