Garmin software? Are you talking about apps and programs that Garmin provides like BaseCamp or Garmin Express? Or you just want to access the files on the device to get your data or load a course? If the latter... with a few exceptions they all connect as storage or portable devices so your file browser should be able to grab the files you want or load them. Typically activities (the log of your ride) are found in the /garmin/activity some devices have it as /garmin/activities
To load a course, copy a .gpx, .tcx or .fit to the /garmin/newfiles folder. However some devices can't handle all of those formats for importing and the file has to be a properly formatted course file. Just because it has .gpx .tcx or .fit at the end does not mean it is a course file.