There are a few very good sources for additional information about how to set up and use Dynamics GP:

Accolade Publications has been around for years. They have a solid set of books to enlighten you on the inner workings of GP. You can see their stuff here: http://www.accoladepublications.com/

Recently two Dynamics GP MVP’s have each published new books about GP.  Check these out:

Microsoft Dynamics GP 2010 Cookbook

Microsoft Dynamics GP 2010 Implementation

If you get stuck while you’re setting up Dynamics GP, reach out.  There’s a lot of good help available.