If you are talking about adding trails to the maps what you need to do is edit OpenStreetMap to add the trails. It is best to record a trip along them so you can accurately trace them into OpenStreetMap.
At some point they will appear in the Garmin cycle maps after an update. If you want to see them sooner you will have to use a third party map that is updated more frequently.
If you want to create a course on your Edge for a newly ridden trail - do following: -ride and record the newly cleared trail - save the activity -open courses menu on your Edge (navigation - courses - saved courses...) -"create new course" (top line of list) -chose the ridden activity - give it a name -that's it!
