The tutorial section gives you help on a number of topics: animation, game development, compiling Orx, setting up projects, tips and techniques.
The config section details what the config system is, what each of the sections and properties are, and how they are used to set up the configuration data in your Orx game or application.
The reference section gives greater detail into all the classes available in orx. Class information is available in the API (http://orx-project.org/orx/doc/html) but the reference section gives more details on the overall classes and their purpose. It also contains links to relevant tutorials and topics for specific classes.
Reference will eventually be retired, and parts will be moved to other sections.