Once you enlist in the Navy, you'll be headed off to 8 weeks of Navy Boot Camp. Like the Air Force, there is only one location in the country that turns civilians into sailors - the Great Lakes Naval Training Center, which is located about halfway between Chicago and Milwaukee, on the western shore of Lake Michigan.
Unlike most other services, however, Navy Boot Camp takes place mostly indoors. You'll do almost everything, from drill to the confidence course to firing shotguns and pistols inside. Indoors doesn't mean easy, though, the Navy is probably the most classroom-intensive basic training course, with lots to learn and lots of tests to take.
Try to learn as much as you possibly can before you leave - things like Navy ratings and rank, the Navy Core Values, the 11 General Orders for a Sentry, the Navy Chain of Command, the phonetic alphabet, are all relatively easy to learn on your own. The more you know before you leave, the less you have to learn in the classroom!
In addition to getting into shape before you leave, try to know how to swim! It seems obvious (especially if you're joining the Navy), but if you are unable to pass the swim test given when you first arrive, you'll require some extra attention. One thing you'll learn quickly in Navy Boot Camp is that extra attention is usually something that is best avoided!