From CreativePro.com –Illustrator’s Other Drawing Modes:
If you use Photoshop, Illustrator, or InDesign, you ought to be familiar with both stacking order and layers. Generally speaking, layers let you segregate groups of content, while the stacking order refers to the order in which items are placed on a particular layer. Illustrator has a few additional options for working with the layering of objects on the page. In addition to the Normal drawing mode, two others – Draw Behind and Draw Inside – can save you time in creating objects in your preferred order…