The sidebar presents everything you've written in a hierarchical fashion. The hierarchy is by no means set in stone. You can move your projects around with ease.
Positioning in the sidebar is determined by the Title and the Category. Both can be changed while editing a page.
The titles are grouped together by category. For example, this page's title is "The Sidebar", and its category is "Docs". Sharing the category is "How Do I", a page which describes the basics of text formatting.
Shifting items from one category to another is as simple as editing the page and changing the Category text field.
The hierarchy has no limits on depth. Pages can be nested under each other by setting the Category of the lower page to the Title of the higher page. You can even make loops!