Follow the in-game tutorial...

Detailed instructions are here

Build custom robots in your browser with IncrediBots! Design your robot by drawing shapes, joints, motors, and more! Then, pilot your machine using your own custom key bindings. How will your robot fare in the hurdles challenge? Or archery? Or off-road? And if you�re not the competitive type, you can record custom movies using �Sandbox Mode� to share with the world. Use the editor to tell animated stories, create Rube Goldberg machines, or just experiment and have fun with physics! The sky�s the limit with IncrediBots!