How do you use a minecraft custom map?

1. Extract the zip/rar/7z/etc. file to:

C:\Users\[your user]\appdata\roaming\.minecraft\saves

2. Make sure there isn't another folder inside your world folder (ex. If you downloaded "Awesome Save" make sure there is no "Awesome Save" folder inside that one. If there is, cut/copy it into the "saves" folder, and delete the empty folder.)

3. Play!