I've had a couple MRI done. The exact procedure depends on what part they're looking at. In my case, they were looking at both my knees. So I stripped naked (I could have kept my underwear, but didn't see the point since I'm not especially modest), put on the ridiculous gown, and laid down on this movable table thing they have. The tech came in and set up a series of pillows or bolsters or whatever you want to call them, so my knee was immobilized. Then it took about 45 minutes as the machine made a lot of noise and did its work.
You can't have any metal anywhere near the machine. So no watch, dogtags, rings, chains, iPods or the like. I'd guess you'd have to remove any piercings. (I'm sure they'll tell you) They had this "iPod replacement", which was a pair of really awful-sounding acoustic-tube headphones (like the ones you listen to on airplanes). The best music they had was a Frank Sinatra greatest hits collection.
If you can, just take a nap. No pain, just a little discomfort in that you can't move your limbs while the machine is working.