Interested in my ancestry

Hi! I'm a 19 year old guy from Norway who is very interested in reasearching for my American ancestors. Here the other day I spoke with my grandma and my great-grandpa (yeah, he's actually still alive - 93 years old), and they told me about relatives (waaay, way back in the old days) in the USA who owned big farms up in Minnesota, and something about this lady being a archbishop or something in New York. Quite interesting! Still though, I haven't had a chance to gather up any useful information to start looking or getting help. How can I do this? If anyone would like to help, here's what I can tell you. (Dunno if this is worth anything at all though) It's on my Mom's side. Their surenames would either be Solli (great grandpa's lastname) or Rausand (grandma's lastname). My lastname is Magerøy, thoguh I haven't heard about anyone on my Dad's side emigrate to the US. I know this is very roughly considering the information, but I'll try to check up more as soon as possible. Most likely we're talking many many many generations back, but that doesn't matter. Thanks for any possible help!