I'm a rower on my school's team, so a bit of insight: the rowing machine is really for one thing, rowing. There are plenty of great workouts you can do, anything from long steady state to high intensity intervals. But if you're just starting out on the erg, you have to commit to learning the techniques and fundamentals of rowing. Not to turn you off from trying out the sport, but to tell you better what you're getting into. If you're still interested, start by googling some tutorials on erg technique. You should be able to find some good videos from some respectable crew teams. For workouts, you can do anything from pick a preloaded workout on the machine, to googling "erg workouts" or something. I think concept 2 (the company that makes the machines) has some good exercises on their site. PM me for rowing questions if you want, and welcome to the club! PS I second nemo. If you want to get generally fit, do SL 5x5.
So I'm hearing a lot about form and different machines, but why is rowing so good for you?
Yeah, technique has been something I've been reading up on.. What interests me about rowing machines is that rowing is a compound exercise. I'd like to create a full-body workout based on mostly these kinds of movements (including chin-ups, pull-ups, etc.). I'm looking for general conditioning of course, but more than anything, functional strength.
There are some good crossfit-type circuits out there, with something like Row, squat, pushup, crunch, repeat in different amounts. Those'll beat hell out of you, not something to do every day. If you're looking for conditioning, make sure you integrate other exercises, particularly running. Rowers, kind of famously, can't run at all, so make sure you don't end up like us.