The book is all about motivation. It explains why the old way of carrot & stick does not work any more. And it shows the new motivation based on three pillars: autonomy, mastery and purpose.
I will not repeat what the book says, I guess you already know it from the famous video (see below). All I want to say, is that even if you know the video, the book is still worth your time.
The most inspiring thing I have learned from this book, is the tiny little thing somewhere near the end of the book. It is about defining yourself with one sentence. Like, what would you like them put on your grave, or what would you like others to say about you. The author calls it a big question and it really gets big once you try to answer it. I tried and I answered it. And it explained to me why I do things the way I do, and it helped me to choose what to do next with my life. I hope it helps you as well.
All in all, this is a great book. Doesn’t matter if you look for motivation for yourself, or you wonder how to help your team. In both cases you will learn something valuable. Read it!