The basis of each installation is the configuration of a project. A project is usually a website. There you will define the default settings for each specific project, e.g. the language and the template design you want to use for your project.
You will also define the url(s) your project is reachable. The different configurations are identified by one of the urls you specified when a user is typing them in a browser. The first url in your list is your main url which controls the paths for hyperlinks and the internal file paths. This feature enables you to manage multiple projects in one installation, for example for different language versions of a project.
The content pages to a project are identified by a root page, which identifies all subordinated content pages. There is no limit up to the levels you create. This tree structure of content pages is also used to build the navigation panel.
The structure of contents is basically divided into content pages and the contents itself. The tree structure displays content pages. In these pages you will define what kind of page it is, e.g. you will define if this page is a plugin or a default content. The content itself can be created in a separate view.