Choose a color from your donut pallet and draw! Up arrow to grow the pen size, down to shrink, and space to clear.
This is a very unique drawing program for a reason. If you draw with blue, then choose yellow, then if you want to draw with blue again you do not have to go back to the pallet. You are able to grow you blue drawing by simply click the blue drawing that you have already done and continue what you have done. I call this "The Donut Spread Technique".