"You've probably used the Pathfinder panel to combine shapes and make new ones. But do you often find yourself clicking (and undoing) each icon in the panel until you get the look you want? Wouldn't it be easier to take some time and learn exactly what each function does? Here's a look at the über-useful Pathfinder panel. The Pathfinder Effects, which are found under the Effects menu, are covered in video format in this tutorial." - Cheryl Graham

Here is a link to Part 1 of this tutorial A Comprehensive Guide to the Pathfinder Panel Part 1 and the video version Part 2 is below.

Illustrator Pathfinder Effects