GPX is an open file format for transferring GPS data between software applications.
The file can be opened in PC mapping applications such as Memory-Map,
Anquet and Google Earth,
in some smartphone apps such as Viewranger,
and can be used to transfer the route to Garmin, Satmap and similar GPS devices.
For MemoryMap, Viewranger, etc, and for older Garmin devices, downloading a separate route for each route on the map usually works best.
Newer Garmin devices (such as the Edge range) handle a single track better.