I installed both Curseforge and the other required mod. I had it all for 1.12.2 as thats the latest version of Galacticraft. I had to make my own Mod folder in %appdata% > .minecraft but other than that, I think it should be appearing.
Sorry, it turned out that there was a mods folder, and I simply hadn't put Galacticraft in it. Very good mod however! I used to play with this mod all the time when I was younger