'Up' to make the pen bigger, 'down' to make it smaller. 'S' to stamp the cursor (P.S. Do NOT ask why this feature has been implemented. I have no idea.) . 'Space' to clear the screen. 'Left' and 'Right' to change colour. Box in top right shows what colour you have. Box in top left shows the size of the pen.
MASSIVE(ish) UPDATE! Didn't do much, but completely changes the possibilities! Now you can change the colour of the pen. And see what colour you have, and what size the pen is.... YOU CAN ACTUALLY DRAW!