In this lesson, I learned about the three different drawing modes and their purposes and how to use them.
Heading towards the bottom of the Tools Panel, there’s 3 little buttons. These represent the different drawing modes available to you.

By default, the Normal drawing mode is selected. The one to the right is called Draw Behind Mode which allows you to draw behind all of the shapes in the document or draw behind the currently selected shape. Finally, to the right, we have Draw Inside mode which means you can draw inside the currently selected objected.
To work with a Drawing Mode, select a Shape Tool, then click on a Drawing Mode.