Use the navigation on the right, which lists all the available mods.
Each mod page itself contains a download link to a zip-file or an exe-file.
Mods must be installed or unzipped into your Blitzkrieg\Run\Mods folder. If you don't have such folder yet, then create it.
After the installation or unzipping, you should be able to select the mod under the Load Mods in the game's Main Menu. In case you can't select it there, check in your Windows Explorer whether the path to the mod is correct. This path should be for example Blitzkrieg\Run\Mods\Modname\Data and not Blitzkrieg\Run\Mods\Modname\IUMII\Data or Blitzkrieg\Run\Mods\Mods\Modname\Data.