Online Genealogy is a fun hobby that is increasing in popularity. It use to be a hassle trying to contact libraries and record halls by mail or telephone.
The "Idiot's Guide..." will show you everything you need to know to get started setting up your family tree. Make sure you have as much detail, about your history, available when you begin your search, to make things easier.
If you already belong to a genealogy club, this book might seem redundant. But it is a nice reference to have when you don't feel like searching your bookmarks for a specific page.
I bought this for my mother, and she found it very useful. Of course she still writes half of her bookmarks down on paper.