I'd guess that a saw is one of the oldest tools man has used. A knife evolved into a chisel and a rough bladed knife probably got used as a saw. Thank goodness foe evolution because now we have two types of saws to use. Those that cut on the push and those that cut on the pull. For discussion most of us use a western style saw that cuts on the push, and it is probably one of the first tools any of us used.For a really simple tool, it is very complex. Here is a primer/tutorial that deals with the basics and complexities of a saw.
http://www.vintagesaws.com/library/primer/sharp.htmlThe article is really geared toward the sharpening of saws however the information is very basic about how saws work and do their job.