If you want an interesting book about the lore of sourdough - and the experiences of Don and Myrtle Holm, this is a great book.
If you want authentic, useable, sourdough recipes this is not your best choice. All the recipes use baker's yeast in them. Baker's yeast wasn't available to the sourdoughs who made sourdough famous, and it doesn't belong in sourdough.
Don and Myrtle admit you can make sourdough without adding baker's yeast, but they get vague on the details. I'd rather stick to a purist approach to sourdough and just use sourdough to raise and flavor my bread, and for that goal, this book was disappointing.
Instead, look at the books by Ed Wood, Peter Reinhart, or Allan Scott and Dan Wing.