It's a really simple ServiceWorker exercise. No build systems, (almost) no dependencies. It's designed to be an interactive introduction to the kinds of things you can do with ServiceWorker.
Either clone it via git, or just download the zip file.
If you already run a web server locally, put the files there. Or you can run a web server from the terminal for the current directory by installing node.js and running:
npm install
npm startVisit the site in Chrome (http://localhost:8080 if you used the script above). Open the dev tools and look at the console. Once you refresh the page, it'll be under the ServiceWorker's control.
You can reset the SW & caches at any point by navigating to reset/. That will unregister the ServiceWorker & clear all the caches.
Disable your internet connection & shut down your local web server.
If you refresh the page, it still works, even through you're offline! Well, we're missing that final JavaScript-added paragraph, but we'll fix that shortly.
Take a look at the code in index.html and sw.js, hopefully the comments make it easy to follow.