How to enable mods?

So I've just got the AOEIII DE edition after not playing this game for quite a time now...its amazing!

But I've installed some mods namely some campaigns and custom maps. When I go into single player mode i.e skirmish to enable them, they're not there. It's not even showing up in the scenario folder

Tried to search on youtube but there doesn't seem to be a tutorial for downloading mods directly from AOEIII DE. I have the installed Aztec campaign but I'm lost as to where or how I enable the campaign to directly play it.

Please help!