This book introduces the fundamentals of blues chords and basic 12-bar progressions. It is on the beginner side, and while it provides a great basic course on blues styles and chords, it doesn't pay much attention to rhythm patterns, and theory is given out in small doses.
The book has progressions in different keys to get you going with a variety of styles, including your basic slow blues, shuffle rhythms, swing & boogie, riff blues and some cool jazz stuff, etc. Most examples are moveable chords, so it gets you playing all over the neck. The explanations are low key but pretty good, pointing out info on the sounds and tonality of the different chords, and some advice on getting a good sound.
There are also sections including some generic but cool turnarounds and intros, and a couple pages about soloing.
Don't think you'll be blazing open mic night after this book, but you will have a good foundation in chords and 12-bar progressions.