To retrace is to walk the same path again, or to follow a path someone else has taken. You could visit the town your ancestors came from and attempt to retrace their steps there.
When you lose your glasses, some helpful person may ask you, "Did you retrace your steps?" What they're suggesting is that you walk everywhere you went earlier, checking as you go to see if you left them on a table or desk nearby. A detective will also retrace someone's steps to solve a crime, looking for clues while walking where the suspect walked. Trace means "outline," but also "follow a line or a path."