
Here's how Sidewiki works; start by installing the latest version of the Google Toolbar. Find the little Sidewiki button in the toolbar and click on it. When you click the Sidewiki button a left-hand column will appear on whichever page you're viewing at the moment. In the left-hand column you can write in your comments, annotations, and edits to the content displayed on the page you're viewing. If other people have done the same, their comments, annotations, and edits will also appear in that left-hand column.

The video below provides a short overview of Google Sidewiki.
Applications for Education
Google Sidewiki could be a useful tool for teaching lessons on evaluating value, bias, and legitimacy of a website. The sidebar could be used as a place for students to comment on sections of a website that they identify as containing bias or inaccuracies.