Create a new folder on your desktop named Les Cent Jours and unzip the download into it, don't worry about going into it because you are going to move the whole folder into the Mods folder
Go to your Computer C drive/program files x86/steam/steamapps/common/scourge of war waterloo/Mods double click on the Mods folder to open it and move or copy the folder Les Cent Jour that you created into the Mods folder, then exit.
When you launch your game click on the Modifications Tab on the first screen and make sure there is a checkmark next to Les Cent Jour and uncheck everything else except the Grog Toolbar if you use it, then click use selected Mods.
Enjoy!!!