Same type of thing, except you're not going to be replacing files, just adding them. Put the map file (it'll end in .bsp) in \esf\maps. The map might have dependencies, but if the mapper was wise, he'd have archived them so that you just have to unzip the package to your main ESF folder and it takes care of the rest.
As long as the map was made correctly, it should show up in your map list to be played on.