trying to load a map from gps file depot to base camp. file downloads well to my C: drive but I can't get it moved over to the base camp program. tells me I have no files selected I think.
Most of the maps here have an installer that should do everything for you. It doesn't matter where the files are stored really, you should never mess with them directly. It is data that Basecamp uses internally.
See this tutorial. This is how a normal install would go. http://www.gpsfiledepot.com/tutorials/how-to-open-maps-in-garmin-basecamp/