For an interesting and concise page devoted to answering questions about what a Stage Manager does checkout How to Become a Good Stage Manager.
For more stage managing tips check-out Managing the Show.
For a brief primer on set construction see this page on Wikipedia - loaded with lots of links of its own.
Want to know more about props? Check out The Prop Shop.
For tips on making the sets look great go to Painting the Scene.
What would the theater be without lights? Here's an article that will get you thinking about how to approach a script and enhance the mood with proper lighting beginning with A Dark and Stormy Night.
And to sound in-the-know and speak the speech of backstage -- check out this collected Glossary of Theater Terms.
Be sure to share any favorite informational links that you may come across for helping tech a high school show.