Well you will need to find data for the trails that you want. This could be a track that you record on your GPS, a shapefile that you download from the web or you could manually draw them on top of the image of a USGS map or aerial photo.
After doing this, you can choose an option to make the map transparent. Note that all of the program features should work on the PC with the free download, but you must purchase the program to actually send a map to the GPS.