Install gpsbabel via apt-get
sudo apt-get install gpsbabel
Connect the gps via the cable provided to the serial port of the computer or via a serial to USB converter to the USB port on your desktop/notebook. To extract the infrormation all you need to do is, execute the following command:
gpsbabel -r -t -w -i garmin -f /dev/ttyUSB0 -o gpx -F data.gpx
The above command copies Routes(-r), Tracks(-t) and Waypoints(-w) from a garmin device (-i garmin) located at Serial-USB interface (-f /dev/ttyUSB0) and saves the info (-o) in the standard gps format (gpx) in the file data.gpx. You can omit the information you dont require and even choose other fromats like kml for google earth:
gpsbabel -r -t -w -i garmin -f /dev/ttyUSB0 -o kml -F data.kml
You should now have a file “data.gpx” which can be used to retrive or map your gps data.