I have no clue as to how to install new unit, city or improvement skins; they don't work when I try to load them from mods. Can someone help me?

I have no clue as to how to install new unit, city or improvement skins; they don't work when I try to load them from mods. Can someone help me?

I suggest checking out the tutorial section of this forum. There's plenty of stuff there.

You might start here