The book is practical & engaging with it's hands-on exercises covering the basic features. The authors highlight important points & offer troubleshooting tips at appropriate places, such as this one -
You can save documents directly to a document library by specifying the HTTP location in place of the hard drive, such as http://wideworldimporters/SharedDocuments/. Only saved documents can be attached to list items as attachments.
This book answers all the HOWs of WSS but not the WHYs and for that you will need another resource. However, after finishing the 16 chapters of this roughly 500-paged book, you'll learn enough to get going on your own. I recommend this guide to beginners. Even after you finish reading it, it'll be a good reference to go back to while you are working on Windows SharePoint Services 3.0.
Also see:
Free Sharepoint 2007 goodies on Microsoft e-Learning
.