I just got a Garmin Montana 710. Which maps do I need be able to use the Roads & Trails feature? I want to be able to create routes using pavement and gravel/dirt roads. I am not tech savvy BTW!
You would want a routable map for that. Go to the "Custom Maps" link above and check the "Routable" box where it says "Search by map features". The selection is pretty limited and I don't have any experience with any of them myself.
Garmin should be able to sell you several routable maps, including the city navigator series (mostly for on-road navigation) or their topo maps, most of which have routable roads (I think, but it's been awhile since I looked at their selection). Of course, those will be expensive and copy protected such that that only work on the first GPS they are installed on (in most cases).