This is a generative drawing tool, where you can control the color (U), size (I), shape (O), and speed (P) of the pen, but direction not that much. To nudge the pen in a certain direction use W,A,S,D controls, and to let it do it's thing, press Q. To change background color, chose a color in the color picker and hit ESC(this will also reset the drawing). Finally, to save your drawing, hit ENTER.