This page provides you with resources for jump-starting your knowledge of Shibboleth and Single Sign-On (SSO).
Internet2, which is the sponsor of the Shibboleth project, has a substantial documentation site with information about how Shibboleth and Single Sign-On work. The extensiveness of the site should also cause you to pause and realize that Shibboleth is complicated software, and using it requires commitment on your part to understanding how it works.
The following Shibboleth documentation pages provide a great start for getting up to speed with Shibboleth and Single Sign-On.
In order to fully understand how a technology like Shibboleth is possible, it is essential to understand some basic web technologies like sessions and cookies. The following are two Wikipedia articles on HTTP sessions and cookies.