Really confused on how this works

I found your site and I successfully had a .zip file sent to me. I had the file downloaded to my Mac, and my Garmin nuvi is connected via USB. But I dont see how to install the map file(s) to the Garmin GPS unit. I can drag and drop the gmapsupp.img file to the device and the SD card, but its very unclear where this goes, or how. Just dropping it in to the “Garmin” folder seemed to freeze up the GPS, so that doesnt seem to work. Clearly you all know allot more about this way of working and I have no clue, can you explain in laymans terms? I have looked through this forum, the, and the but nothing seems to clearly explain how this is done. I need this to work before traveling abroad in two days, so fast assistance would be much appreciated. Thanks

Did you read the manuel?