Which mod are you trying to get to work? The correct installation depends on what kind of mod it is, but the description usually states, if the Mods-folder is required (standard path is C:\Program Files(86)\Stardock Games\Galactic Civilizations II - Ultimate Edition\Mods or C:\Program Files(86)\Steam\SteamApps\Common\Galactic Civilizations II - Ultimate Edition\Mods, I believe, if you use Steam).

If the Mods-folder is required, extract the mod there. You should then be seeing it alongside the standard ones (Default and Example) in the list, when trying to change the mod directory in the game options.

The description for Autumn Twilight should say "Bugfixes and balance changes for Twillight of the Arnor", so there is definitely something off.

Have you extracted the ZIP-file? There should be two new folders in the Mods directory, if you did that, Autumn Twilight and Campaigns. (The latter folder is only important, if you actually play the campaigns. In that case, you need to move it to the Twilight\Data\English folder. Otherwise, you can either ignore or delete it.)

The Default and Example mods have the same description, so that is okay. It's weird, that Autumn Twilight shows the same though.

You said, that you changed the Mod path in the prefs.ini, right? If the path is correct, then the mod should already be working. Have you tested if that is the case? When selecting a race, take a look if any of the races start out with the tech Capitalism (or Black Market Dealing, in case of the Korath).

Ok, I got it to work! I found the Capitalism with the Humans. The Yor has Hyperwarp. For some reason, I have two locations for Mods for ToA. I changed the path by taking out the "Twilight" sub folder. Your Mod description finally appeared! Thanks for all your help!