The getting started with umbraco post is the most visited one on this blog. I thought I would make an update since getting started with umbraco got a lot easier recently because there are 9 free videos on umbraco.tv outlining the basics for both site builders and developers. Learn about the basis building blocks like document types, templates and macros and also see how easy it is to use .net user controls.
You can find the free umbraco foundation videos on umbraco.tv
For site builders:
These should be your first stop when diving into Umbraco!