NB This tutorial is specifically for Star Trek Armada 3.
Nonetheless the priciple applies to most if not all Sins mods
Always read the README.txt file with any mod first.
There is a common bug within Sins of a Solar Empire that with some mods the in game feature to enable a mod wont work. To combat this alot of Mod Dev teams include a file and instructions to manually enable their mod before you launch the game.
Join Cpt Shack as he briefly explains how to install a mod for Sins manually using Star Trek Armada 3 mod as an example