Scene Nodes
Scene nodes are used to add entities to the scene, and are the most important nodes in the graph.
Camera
Without a Camera, nothing will be rendered because the Camera is the mecahnism to see the world. A Camera node is the minimum you need in your graph for anything to be rendered.
Object
Objects transform and apply a material to geometry.
Light
Lights add dynamic lighting to your scene.
Environment Light
An Environment Light adds Image-Based Lighting to the scene.