What you do is go to your saves (in the minecraft folder), generally %APPDATA%\.minecraft (on windows) or ~/Library/Application Support/minecraft (on mac) put your downloaded map in the folder, then unzip it. It should appear, it can sometimes be on the bottom of the worlds list.
My advice is to use another pack as a template (unzip it and you'll see) Make sure you delete all the assets from the original pack after. then send it to a zip file.