When it comes to figuring out how the system works, BumblingBear is off to a good start. If you want to get a better feel for how the rules mechanic works, I would suggest looking up the System Reference Document (SRD) for Spirit of the Century or any other Fate system. While The Dresden Files is different in some ways, you will realize that the general approach to the rules and the thoughts on roleplaying will generally be the same.
Now, when it comes to finding a group, you have a few options:
1) Find a local brick and mortar store. Comic shops, hobby shops, and various game shops may already have an RP night in the works, and you'd be amazed at how many people you would find that way. Even if you won't play the DFRPG right from the get-go, you might find some that may be interested.
2) BumblingBear and crusher_bob are on the right track: use the internet. There are many Play By Post boards, as well as RP groups galore. Go out and have fun!
3) If you are a college student, see if you have some form of gaming or anime club. Many of those people travel in the same circles, and you'd be amazed at how these people pass their time, but be warned: working with them may be like herding cats (I should know; I'm the advisor for the combined Anime Gaming and Roleplaying Organization at my campus).
4) After you get your books, grab some of your friends, even if they aren't entirely into either Roleplaying or Dresden, and just host a game night. Read up on the rules, snag the Neutral Grounds adventure, and let it loose! One-shot nights are always a blast, so keep that in mind.