What is TCX?
TCX is Garmin's training format: a GPS track with heart rate, cadence and lap structure wrapped around it. FileSorcery reads it and converts out. Writing one is deliberately not offered, because a schema-valid TCX needs activity timestamps that a converted file cannot honestly invent.
What is KML?
KML is Google Earth's format, and by extension the one most mapping tools will import without argument. It describes placemarks, paths and polygons, and it can carry styling - colours, icons, line widths - alongside the geometry.