Instructions
Follow link in the Resources section to the official LEGO website.
Click "Download LDD 4" on the right side of the page. Choose your operating system and click "Download." The application takes about 120 megabytes of hard disc space.
Follow the directions to install and run the application.
Choose "Design by Me" to create a new LEGO design from scratch. Select "Mindstorms" or "Creator" to start with a complete set from Mindstorms and Creator sets, respectively.
Select the elements you want to use for your design by clicking on the "Bricks," "Templates" or "Groups" on the left of the screen.
Click the navigation arrows to look from different angles at the 3D image of your LEGO design.
Click "Design by Me" icon after you are finished if you want to order a physical version of the set you've created. Click "Check Price" button to get an estimate of how much it will cost. Click "OK." You will be redirected to a page through which you can order the customized set you designed.