This layout shows an example of a knowledge-base style navigation system, where there is no hierarchy, just groups of pages that have certain tags.
If you're getting started with Jekyll, see the links in this section. It will take you from the beginning level to comfortable.
This section lists different content types and how to work with them.
Note: This was mostly an experiment to see if I could break away from the hierarchical TOC and provide a different way of arranging the content. However, this layout is somewhat problematic because it doesn't allow you to browse other navigation options on the side while viewing a topic.