Federation Elite Ship Pack addon - Gratuitous Space Battles

If you got this game from steam downloading mods works the same way is if you didn't, your file is just saved in a slightly different place.
It can be found in "C:\Program Files\Steam\steamapps\common\(Chosen Game, in this case Gratuitous Space Battles)", or something similar. If you don't find it in there try "program files (x86)" instead.
This works for most steam games, like oblivion or for mods with fallout 3. For some games, like Garrysmod you need to go to C:\Program Files (x86)\Steam\steamapps\(Your Steam Username)\(Chosen Game)
P.S. I advice going into Computer through the start menu and navigating thru the folders manually, and not copy/pasting what I wrote, because your computer might be a little different.
P.P.S. Always read what mods say, there might be a specific place to put it!
Hope this helps, and feel free to correct me if I made a mistake!

You may have to put the files into each folder manually. For every mod I've installed I've put the files into their respective folder by hand. This is especially true if you are adding ships to existing factions like the federation. Put the hulls, components, and everything else into their respective faction folders. It's worked for me, just takes a little tinkering with the game files