I have seen books which can tell you all the theory about TFS. And yes, what will happen if you click on a button on Branching dialog....that too. But if you really want to know what exactly is TFS, don't just download and forget this guide posted on CodePlex which describes how TFS should be used in real projects. Excerpts from the site:

"This guide shows you how to make the most of Team Foundation Server. It starts with the end in mind, but shows you how to incrementally adopt TFS for your organization. It's a collaborative effort between patterns & practices, Team System team members, and industry experts" 

patterns & practices: Team Development with Visual Studio Team Foundation Server - Home