This is an in-depth overview of creating and using the Ext Grid component, formatting it and hooking it up to a Data Store. It also begins with a nice introduction to setting up Ext and using Firebug. After you finish this tutorial, make sure you watch the follow-up Editable Grid Component. This tutorial was contributed by Ext community member Scott Walter.
You can also download the source files to this tutorial if you'd like to follow along.