My son has studied this subject from scratch, finding the book presented well, easily understandable, going from beginners to mid level complexity. There's plenty of questions at the end of each example with the answers in the back. To use this book you need to know early secondary school basic shapes and a basic understanding of algebra would be helpful.
This is a critical resource to accompany Ryan's main Geometry for Dummies text. Having stated that, the breadth and depth of geometry covered in either of Ryan's texts is likely more than most need unless advancing into calculus.