The website is produced with Jekyll. It allows you to build a reasonably good looking website that is easy to maintain and modular in nature. Templates are used from the _layout and _includes directories which are then used in conjuction with content that is created with Markdown, Textile, or just standard HTML for input. Using Markdown or Textile allows the content to be generated with simple rules that allow a more free flowing process of writing without worrying about coding for the HTML.
To get started please read the Jekyll website for installation instructions for that tool. After installing Jekyll you need to get the website project. This is available from the same git repository that the main source code is, it's just a different module, www. Checkout this module and then within the top level directory of the module simply run jekyll build. This should produce the website in the _site subdirectory.
To add a page the easiest thing to do is copy an existing one from the site like
and then rip out its contents. Once new content is created and you have saved
the new page you will need to add the new file to the menu system
of the appropriate _includes
A good place to look for example content is Jekyll's wiki site where there is a listing of real sites that use Jekyll. Many of these sites will have their repositories available for review.