Similar to https://gist.github.com/charliepark/3171750, this is CSS / JS for using a Gist as a datastore, without relying on the Gist / GitHub API.
Why would you want to avoid the API? Maybe you wouldn't. But sometimes it's easier to parse a few lines of JS than to try to fully get the GitHub API. Also, unless you know the name of the file that you're accessing, you have to do some key-sniffing to pick apart the JSON and get your file contents if you're going the API route. (You can see more about how to do that here: https://gist.github.com/charliepark/5054053)
First, you need to know the Gist you'll be using. In this case, https://gist.github.com/5037450. In the head of your document, call it, like so:
<script src='https://gist.github.com/5037450.js'></script>
Note that you're calling the .js version of that resource.