This example is from the Udacity Critical Rendering Path course and is designed to allow you to apply different optimization techniques to optimise the rendering and improve loading time performance of the pages and files.
Start by creating an account (if you haven't used Github before) and then fork this repository by clicking on 'Fork' on the top right corner of this page).
There are different ways to use Github, but we are going to keep things as simple as possible. Start by reviewing the current PageSpeed Insights score by finding the URL of your forked repository (e.g. https://github.com/benjaminmangold/mobile-portfolio/master/index.html), copy everything after the domain (e.g. /benjaminmangold/mobile-portfolio/index.html) and adding it after https://rawgit.com – so that it becomes: https://rawgit.com/benjaminmangold/mobile-portfolio/master/index.html
This new URL allows you to navigate to your page and preview changes that you make to the code. (Please note that changes can take a few minutes to be reflected on the rawgit.com domain.)
Now you can navigate to https://developers.google.com/speed/pagespeed/insights/ and enter this new URL to see the current score for the page.
The objective is to apply the techniques covered to improve the score of the page.