The server support various minimaps. Here's a guide for getting Forge, Zaero's Minimap, and OptiFine setup.
Great, now Forge is working. We can move on to installing the mods.
.minecraft folder, on Windows you can type %appdata% in the Run dialog to find it.
Xaeros_Minimap_*_Forge_*.jar file in the mods folder.
That's it! You should now have a working minimap installed.
OptiFine_*_HD_U_*.jar jar file.
Note: if you have previously installed OptiFine you'll need to navigate to the %appdata%/.minecraft/mods folder and remove all but the latest version.