Instructions
Right-click the mod file you downloaded and select "Copy" from the context menu.
Navigate to the folder on your computer where "Europa Universalis" is installed and open the "MOD" sub-folder. The default installation folder is "C:\Program Files\Paradox Interactive\Europa Universalis III" although this might differ if you bought the game from a digital distribution service such as Steam.
Right-click anywhere inside the MOD folder and select "Paste" from the context menu to add the mod file.
Right-click the mod file and then click "Extract Here" to extract the contents of the archive. For this option to appear, you must have a file extraction utility such as WinRAR or WinZIP (links in Resources.)
Double-click the "eu3.exe" file in the game installation folder to open the launcher. Do not launch the "eu3game.exe" file as this opens the game.
Click the drop-down list below "Select mod to play" on the launcher window, and then select the mod that you want to run.
Click the "Start EU3" button to launch the game with the selected mod.