This tutorial is an advanced guide covering how to use the Magic Extractor to change background in Photoshop. The Magic Extractor is an incredible useful tool, and something that can be used for many art projects.
To open up the Magic Extractor, go to Image> Magic Extractor.
First of all, let me explain the uses of the various tools in the Magic Extractor. I've composed a list and made a diagram to make it as clear for you as possible. Click on any the images in this post to see a larger version.
Diagram of main tools in Photoshop's Magic Extractor