In this recipe, we'll see the properties and the settings of the World in Cycles.
The main characteristic of the Cycles World is that it can emit light, so it practically behaves as a light source. Actually, its effect is the famous Global Illumination effect.
As in Blender Internal, the World is considered as a virtual dome at a large distance from the camera, never touching the scene's objects. Nothing in the 3D scene can affect the World. Actually, only the World can emit light on the scene and the objects.
start_04.blendfile and go to the World window under the Properties panel to the right of the screen. This is where we see the usual Use Nodes button under the Surface tab.