If you're just starting out with Drupal, this book is an excellent introduction that will help you get up and running more quickly. Written for beginners, it gives a nice overview of what Drupal is capable of and step-by-step instructions for setting up a basic installation.
Drupal is a powerful, world-class content management system that happens to also be open-source (read: free, agile and very well-supported). If you're thinking of taking it out for a spin, you'll find Mercer's book a huge help. The Drupal community does maintain "handbooks" on the site that cover most of the same material, but Mercer goes into much more detail, especially on basics that might otherwise stump a beginner. You won't find much on more advanced features or customizing Drupal, but you will gain a solid understanding of Drupal's basics—which is a good foundation for beginners who hope to move on to more complex Drupal work in the future.