It is in the PDF format, so you'll need Adobe Acrobat Reader in order to read it. The official World Builder manual written the the development team. It has been written by the community member RVMECH, who designed some of the maps that have been included in the game.
CNC Den has an excellent tutorial for those of you new to World Builder. The editor has a slightly bigger learning curve than the map editors for older C&C games (such as Final Alert and Final Sun) but offers more functions.
