StumbleUpon was founded in 2001 by four people named Garrett, Geoff, Marc, and Mark. It is a web 2.0 tool that allows users to discover, rate, and share new web pages based on their personal interests by stumbling from page to page. The document provides tutorials and steps for how to join StumbleUpon, explore the toolbar, set up a profile, make friends, use StumbleVideo and StumbleThru features, and enable search reviews. It discusses the pros and cons of using StumbleUpon, such as free traffic but time consuming without targeted traffic.