The workspace panel, once again, has a layer stack for working with textures called Materials. Similar to other modes we need an active layer for our tools to work.

So before we can work with textures we must have at least one material layer armed, and have a zone assigned to that layer. Go ahead and create a couple of material layers; call them Beach, Plains, and Mountains.

Terrain textures are rendered as layers in the order they sit on the stack. The top-most layer being rendered last.