Overview of Materials in Cycles - Blender 2.6 Cycles: Materials and Textures - page 21

How to do it...
However, to have access to all the options for the World , we have to initialize it as a
node system:
1. Look in the bottom header of the Node Editor window, on the left-hand
side of the material datablock, there are two little icons: a little cube and
a little world and, yes, the cube icon is used for creating materials, while
the world icon is for the World window. At the moment, because we were
working on the spheroid material, the cube icon is the one selected.
2. Click on the little world icon. The material's node disappears and the
Node Editor window is empty now, because we entered the World
mode. Check the little Use Nodes box on the right of the datablock to
make a default world material appear. Or else, go to the World window
under the Properties panel and click on the Use Nodes button under the
Surface tab, as shown here:
Also, for the World , the default material is simply made up of two nodes:
a Background node connected to a World Output node. In the Back-