Scenes can be presented like invisible layers, similar to layers in Adobe Photoshop.
Their structure is very easy to understand. They are composed from Components and Subscenes.
Subscenes are common scenes but they are linked with their parent scenes. This means that changes in scenes can affect subscenes. For example, when you move scene, subscenes will move too. Subscenes are always rendered on top of parent scenes. It means that you can not use some subscene as background for parent scene.