Set the variable sliders to any number you like and then click on the draw button to draw. You can repeat as many times as you like. You can get some fairly cool patters by layering drawings on top of each other. If you want to clear your drawing, click on the green flag.
I was actually just playing around with the drawing and make your own block tools when I wrote this. It turned out kind of fun, so I thought I would share it. Have fun and feel free to remix.