Garmin GPS devices typically come packaged with their MapSource Trip and Waypoint Manager software. It is used to move maps and waypoints from your computer to your GPS. In my experience the MapSource software works but it seems to be geared more toward on road use rather than on trail use.
Thankfully, Garmin now has their BaseCamp software available to download for free. BaseCamp is a more wilderness oriented product that offers some very nice functionality for those who take their Garmin GPS outdoors.
The best feature of BaseCamp for me is how easy it is to create routes and waypoints. You can plan an entire trip on your computer before you ever set foot on (or off) a trail. There is also support for Google Maps and Google Earth. BaseCamp lets you print professional looking maps that even have automatically generated map details, lat/lon or UTM grid lines, magnetic declination information, and maps scales. Sadly, the maps do not necessarily print in a common scale, but they are still very useful. I have found that it handles large topo map sets much better than MapSource Trip and Waypoint manager. It works great with the free maps from GPSFileDepot.com.
Garmin updates BaseCamp fairly regularly and there has been talk of upgrading the printing so that users can print in common scales like 1:24K. Product support and free software like BaseCamp is part of the reason that I own several Garmin GPS units.