You are correct in that someone in the genealogy section in the library probably can evaluate what information you have and give you suggestions for tracing further back. They probably have an Ancestry.com and/or Heritage Quest subscription at the library where they can help you find social security death indexes, census records, etc. that can be used as to clues to trace back. The librarian can give you a little guidance. You can surf for How To's on the internet.

But, do make sure you understand the guidelines of the project and don't stress out if you can't connect yourself with proof to an ancestor in another country that everyone in your family says you're from. Professional genealogists sometimes can't do that in a lifetime. When my son did the project some of the kids focused in just a couple generations back, the family customs that had been passed down, gathered photos, documents, and heirlooms. Others, based on the guess as to when their ancestors came to US used library books to find information about the history and lifestyle during that period of time. If you have to have a display like my son did, see if you can find someone to put your family tree in a genealogy software to print out a chart. If you are interested in cultural food, display a recipe and possibly bake/cook that item. Make maps and drawings of where your ancestors were believed to have lived and/or their migration path across US. Have short titles and pictures about the food, work, houses, etc. that were in that country.

Have fun with it and consult your teacher of course if you think you may be outside of the guidelines for the project.