Product Type use Primer, where is it?

I'm a newbie and I would really like to find a clear and concise primer on just what Product Type is, how it is best used, and how to edit it and/or change it to meet my needs. Does the book "e-Start..." cover this at all. I've bee searching the forums and getting flooded with information that is totally unorganized and I really don't have the time to read everything, some of which is very old and may not even be valid anymore.

I'm Using Zen-Cart 1.3.7 and I've added a free template also.
I have read "Zen Cart—E-commerce Application Development"

The E-Start book has a two-page overview of product types; it is not intended to give developers in-depth info on altering them.
The best reference is probably the wiki:
http://www.zen-cart.com/wiki/index.php/Product_Types