Hello, welcome to the forum.
A lot of our most successful users on here have breastfed. You've also got the advantage of being young. Please don't let your boobs get you down though. None of us on here are happy with our breasts in one way or another, but all of us are stunners!
As for how it works. It works by applying a vacuum to the breast tissue. This increases blood flow to the breasts (carrying hormones, oxygen and nutrients) and by stretching the cells, encouraging them to divide faster. Combine that with good diet and you're growing boobs. (Massage also helps for the same reasons).
It does work. It's a slow, unpredictable process, but it does work. Some people respond really quickly and really dramatically, wheras for some other people it's a long steady progress. But I have yet to see anyone who has stuck with it for more than 6 months who hasn't seen some sort of growth.
Pain-wise. It shouldn't hurt. It might feel a bit uncomfortable at first if you've not got a lot of body fat to protect your ribs and sometimes I find the skin under my armpit gets pinched. But as a general rule, if it's ever too painful you're doing it wrong.
With hand pump you pump until it feels comfortable and the vacuum stays until you release it (by pushing a little button at the side). Personally I'd never want an electric pump as I want to be in complete control. When I first looked at noogleberry I thought you had to pump constantly to keep the pressure up (I thought I'd get really strong hands AND huge boobs), but that's not the case at all.