Here's Google's training info on Google Search Level 1: The Basics and Classroom Application (Level 2). They're easy-to-follow and quite nicely laid out.
You can create customized Google searches that limit search results to specific pages, or specific types of results. This can be really handy if you want your students to do research within some specific web sites that you feel are reliable and useful.
To create a custom search, go to google.com/cse and click the "Add" button to get started!