Click on the paint splotches to choose the colour of your pen. The default (when you click the green flag) is a white canvas and a black pen. The two sprites in the top-left corner change the colour of the canvas (black or white). Click the erase all button to get rid of all of your pen. Click the button on the right-hand side (which looks like a piece of paper...see it?) to find out how to change the size of the pen. Press with your mouse to draw. NOTE you do need to keep holding the mouse down to draw.
