Help starting

Hello, Just got into looking for my birth family. While I do have limited resources for information (seperated from by blood family when little, but do know a few names) I was wondering how to start looking. What I have is...and this is the sum total, Sam and Laura Larsen emmigrated from Bergen Norway with my grandfather Ludvick Ingolf Larsen, born Oct 28, 1925, when he was 5 years old. That would be Ship date 1920. He had a brother Arthur and a sister Ragna. Not much to go on, but it's something. I am finding all of Ludvick's children here in the US. That doesnot seem to be hard, but would like info on how to start researching back from the ship date and info on how to find relatives/heritage in Norway. TIA, Don