Once you've downloaded the .zip file from the website, you'll want to extract the file to your Space Empires
V Empires folder. All empires for Space Empires V are placed here:
If you are using the steam version of Space Empires V, your install may be buried deep in a folder like this:
C:\Program Files (x86)\Steam\steamapps\common\SpaceEmpiresV\SE5\Empires
If you extracted the race correctly, it will have its own folder in the Empires folder:
For adding custom races to the Balance Mod, check out HERE.