Some file types can be imported (*.kml, *.kmz, *.gpx, *.wpt, *.trk, *.rte, *.rt2, *.plt, *.gdb, *.mps, *.bcr, *.freshroute).
Select 'Import...' from the 'File' menu to import one of these file types.

Files cannot be exported to all of these file types, because Tyre is meant to cooperate with Google Maps and Google Earth. It is not meant to be a conversion program.
If you want to convert files, there are lots of other programs available for that purpose at the internet. I prefer GPSBabel from www.gpsbabel.org.