Use the sliders to adjust the pen. Press S to show sliders and H to hide them. The Mouse/Arrow slider determines whether you use the arrows or the mouse to draw. This gets annoying, but whenever you change a slider, you have to press the mouse onto the canvas to make the arrows work, or else you'll change the slider. Sadly, there is no erase.
In my coding class at school, we started learning how to use Turtle (graphics with Python). It takes FOREVER to do anything, so I decided to make almost the same thing in Scratch. This is what you get.