Info is here about how to use a mapsource version [i.e. gmap folder]: [Only registered and activated users can see links. ]. Scroll down to 'Have you downloaded a Mapsource Gmap folder ?'.
In brief, you cannot simply use an unconverted mapsource version directly in any Garmin unit or on a media card, you must use BaseCamp/MapInstall to make a map .img file. Have a good read of that linked thread and others here: [Only registered and activated users can see links. ]. Post in appropriate thread if you need more help after doing thorough reading of them.
Everything basic can be found by searching rather than opening new threads.