GPX Viewer PRO supports importing gpx, gpz, kml and kmz files from device storage or cloud storage like iCloud. It also supports exporting int gpx and kml files. Gpx and kml files contain tracks, routes, and waypoints. Gpz and kmz files are just compressed (zip archives) gpx and kml files respectively. You can find more information about gpx files on this website and more information about kml files can be found on this website.
On this help page, there is information on How to import track or waypoint. Also, there is information on How to export track or waypoint.