For a concise introduction to the zone system, I would suggest taking a look at:

Norman Koren's web page is primarily devoted to digital photography, and has not been updated much in quite a while. But, there is a lot of good information there on various aspects of photography, including this description of a "simplified zone system". I think that Koren does a pretty good job of describing the key ideas of exposure using ZS terminology, but doesn't get into film tests and development.

Hope this helps,