Working with drawing modes
Illustrator has three different drawing modes that allow you to draw shapes in different ways. They are found near the bottom of the toolbar: Draw Normal, Draw Behind, and Draw Inside.
Draw Normal mode: Every document starts by drawing in Normal mode, which stacks shapes on top of each other.
Draw Behind mode: This allows you to draw behind all artwork on a layer if no artwork is selected. If artwork is selected, the new object is placed beneath the selected object.
Draw Inside mode: This mode lets you draw objects or place images inside other objects, automatically creating a clipping mask of the selected object.