The station in Trondheim is located at Dyre Halsesgt. in middle of the city and close to the harbour. From Trondheim there are local, regional and long distanstrain services towards Oslo, Røros, Bodø, Steinkjer and Østersund in Sweden. There are local train services to Trondheim Airport Værnes, use the local trains towards Steinkjer.
Tourist info: http://www.visittrondheim.no/en/tourist/