Go to http://www.rptoolstutorials.net/ for the best tutorials.  They consist of a series of screencasts (made by forum member brad) and are typically rather short -- just a few minutes each.

Because they're broken down into GM and Player videos, each user only needs to watch the ones that apply to them.  Of course, GMs may want to start with the Player videos so they get a feel for what the players will see before they move on to creating content!