While you learned how to make some basic shapes, our world would be pretty boring if it only had rectangles, circles, and squares in basic colors. By experimenting with modules such as the pygame.image() module you can learn how to work with images that are created outside of pygame. If you have an artistic sibling or friend or you are an artist yourself, you can create or scan artwork in your computer and then add it to your games.
Note
You can learn about the pygame.image() module at http://www.pygame.org/docs/ref/image.html.