Use arrow keys to move. Black dot in upper left corner changes color of your pen if you click. Click to draw. Red hurts. Blue is water. Black is ground. Green is win. Pink thing to the right of the black dot is eraser to erase your level, and then comes the restart to, well restart if you get stuck. In the upper right hand corner is an example level of what you can make, click it once to make the level appear, once more to make it disappear.
Updated with: Better pen. Better example level. Better Pen colors. Better system (doesn't erase after you win or lose). Better gameplay. 2 times better than the last :D.