One of the best ways to understand the capabilities of VSTS is to see it in action.  These videos range from overviews of VSTS to specific product feature areas:

http://www.microsoft.com/events/series/Msdnvsts.aspx?tab=webcasts&id=odall

 

Some of the videos are based on VSTS 2005 but the concepts should apply to VSTS 2008.

 

Additionally, Notion Solutions has provided these on-demand webcasts:

http://www.notionsolutions.com/training/Pages/VSTSVideos.aspx