There's a free video tutorial called "image planes and setup" in the tutorials section. Just click the VIP link up top and choose the free tutorials. That will teach you how to setup reference planes. You can also use k-man's helpful refplanes script which can be found in the following thread. When you install the mel script, and type "refplanes" in the command line, a dialog box will pop up allowing you to browse for images being used for the top, side, and front views. Then, it creates the planes automatically. I'm currently working on a modification of it with his help for adding a back view plane as well. You can also move the created planes easily for translating along an axis if the default isn't what you need.