Click and drag the objects. Hold an object and press A to delete it. Press SPACE to create a new object next to the mouse pointer. Hold S while pressing SPACE, to create a generator.
Everything by me. I made a game with this. At the moment it's just a DEMO, but you can love it, if you want more levels and features :) The game: http://beta.scratch.mit.edu/projects/10073927/
