I would add one small suggestion to APTurner's excellent answer. If you have a suspected person, trace his family tree back as far as you can. Then watch for "mother line" matches as well as family name matches for his ancestors. That way you will know that the Ebenezer Smith family of Rockymount NC is a cousin match even if your potential ancestor was living in Ohio and his surname is Jones. If his grandmother was a descendant of that Smith family, you have another part of the tree potentially verified.