All good advice here. The main thing you want is a 'buffer', not a grinder. The difference is speed - a buffer runs around 2500-2750rpm.
I was taught how to detail cars back in the 70's, and have done paintwork and finishing for all these years. The brand is not as critical as just getting a true buffer. The two-handled orbital polishing thing is a waste of money - you may just as well do it by hand.
I have always used a wool buffing pad on a rubber buffing wheel, then polish with a soft polishing 'bonnet'. That's what I 'grew up' with, so that's what I'm used too, and I can get a glass-finish gloss with that process.
Now the new soft foam pads are all the rage, that's what you find in the body shops. The stuff is expensive though, and you have to invest in the whole 'system'.
3M makes outstanding products for cutting and polishing, but the others find favor out there too, such as Meguires, colonite, etc.
Look up a local paint supplier in your area and pay them a visit. They'll help you get the materials you need. I like this company for supplies online:
http://www.topoftheline.com Great products, fast shipping, good prices.
Yes, it's a learned skill, best to practice on something not as critical to get the feel. It's actually more difficult on cars because of the hard edges - novices will invariably burn the paint off! Buffing a hull is much easier, except for holding up the machine for several hours - it's a real killer!
I had an aquintance with a restored 41 Cadilac that was painted black and never rubbed out, the paint was several years old. I wet-sanded it with 600 grit, then 1000 and buffed and polished it. He said it looked like he got a new paint job. It went from a basic re-paint finish to glass in a few hours.