Hi today im gonna show you how to download a custom map

step.1 download and save the map u want to use.

step.2 if its on winrar extract the files to a folder

step.3 go to the folder and copy it

step.4 go to %appdata% and double click on ".minecraft"

step 5 go to the saves folder in ".minecraft" and paste the map u downloaded"

And there u go u just downloaded a custom map!