QED (Quantum Electrodynamics) is a relatively new field of physics, specifying how light and matter interact. It mathematically describes all phenomena involving electrically charged particles interacting by means of exchange of photons.
Feynman is possibly the best guy to write a book about QED, because apart from being a legendary teacher of physics, he's also made direct and important contributions to the study of QED, and won his Nobel prize for this work in 1965.
The approach Feynman picks for this book is "for newbies", although I doubt that newbies will gain much from this book. The concepts are described in them lucidly and I don't think an intelligent reader will have trouble understanding them. But for a reader without any background in physics, the explanations won't mean much. The true "aha" moments I had while reading this book came when Feynman offered an illuminating fresh explanation for some phenomena I was aware of from my undergraduate courses in physics.
The book is very short - only 150 pages of it, and leaves the reader with a large appetite for more. Unfortunately, it's doubtable how much further can be explained without getting into the complex math that's used to describe these topics. Moreover, I wish there was some math in this book, as in a few places it's obvious that Feynman refrains from providing a full explanation because the readers have absolutely no mathematical preparation.
I can't say the book is perfect - in some places the explanations are not very clear, and many topics are left uninterpreted. But it's very good indeed, and I highly recommend it for anyone with interest in physics and "how the world works" in general.