While you can learn a lot from books, the most important thing to learn is how to be safe. For that I'd take a course. The two I know of that offer classes in the U.S. are Performance Freediving International and Martin Stepanek's Freediving Instructors and Trainers. PFI is out of Vancouver, BC but also offers courses in Hawaii, Monteray, CA, Miami, and Grand Cayman. FIT is out of Fort Lauderdale, FL. Martin used to be an instructor/partner of PFI, but split to start his own company. While I only have experience with PFI (after Martin left), I'm sure they're both quality training programs.
Learning to freedive can be very dangerous, even in situations that you'd think were relatively safe. For example, people die in the pool just holding their breath. So the other necessity, if you're going to train in the water, you really need a buddy watching over you.
But that said, I think it's worth it. There's a lot you can do on a breath hold that you can't when you're blowing bubbles. Have fun learning.
JB