1-Download the tutorial files from the free stuff or the WorldBuilder database.
The files are saved in WorldBuilder 3.2, so users who don't have 3.5 can use them too.
3-Open the library with procedural textures by rightclicking in the library window or from the toolbar. (Or load it from the main menu)
4-Drag and drop "Grass&Sand 5" in "Area 1 (full)" of the object tree, or "Area 1 (full) in the property page or in the topviewport.