Click the colors to change into them. eraser to well erase. And use the slider to change size. Press space to clear. press screenshot when you are done with your work, and then take a screenshot. Then press resume when you are done and want to get back to drawing. Warning, if you click eraser and press before you get out the purple zone you will erase the purple zone. If this happens just press clear.
thx to @micromacro who helped me figure out how to do the pen size!
