uhh... download from Civ V. Then, "install", which you have to do in Civ V. When you are in the "choose mod" screen, there is an online tab, an installed tab, and a downloaded tab (these are not yet installed).
So, install the mod.
Then, when you go to setup, choose the map you want to play on.
If there is a specific scenario with the map, which you want to use, then you also need to click on the little button next to the map (blue-like) so that it has a green checkmark.