From the LEGO Factory website:

"LEGO Digital Designer is a virtual design studio that lets you create your own LEGO model right on your computer. Once you've finished your model, you can order the bricks from the factory and show off your design in the online Gallery!"

LEGO Digital Designer (LDD) lets you design LEGO models on the computer using a simple CAD-like interface with 3-D rendering. When you have completed a model, you can upload it to LEGO to share with others and to price and buy if you like. It lets you build your ultimate LEGO creations.