The following tutorials aim to explain ZD Defined classes and how to use them in Reality Editor. 

With ZD Classes, you can expose any blueprint event graph mechanism into "Reality Setup". To give any input/output mechanism you need to understand Unreal Engine Blueprints as well. Zero Density has some classes to work properly with Reality Setup. The main idea of the ZD Classes, exposing any control data mechanism on your view-port, game system or level into the RealityHub.