Just put the pen to the place you want to draw on and hit the draw button. You'll have to place it where you want to before drawing. To stop drawing, hit the stop button. You can also change colors if you want to. When you're finished, place your pen on the finish button.
Originally for the Digital Heart Club project, but that ultimately got cancelled. I thought it fit with the Scratchtober prompt for the day, doodle, so here it is now. Please do not remix this without my permission.