This is the best book I've read on using chords in songs. Without knowing much about chord progressions and harmony, I went to a music teacher for a while who taught me what the basic chords were, but this book really put into place exactly how those chords can be used in a song.
This book uses I, IV, V chord type of notation, with the note (like G, F, etc.) written underneath it. I use keyboard and not guitar so the basic chords were fine but some of the notation was a bit more geared for guitar (I think guitar tends to use G where as keyboard is oriented at middle C). Possibly it would have been clearer if they'd had a version of the book geared specifically for keyboard.
But none-the-less, this book has been a godsend. I'd been looking for a book like this for a long time, one that explicitly shows you the techniques that popular music has been using for years, techniques that someone like me, who does not come from a musical background, can try out and run with.
Again, if you have questions like, what is harmony, what is a relative minor/major, you may want to find out the basics first, but once you know a tiny bit about chords, this book could very well give you a new "aha!" every time you study from it.