The server support various minimaps. Here's a guide installing Xaeros Minimap on 1.12.2.
This guide assumes you are running either the vanilla Minecraft client, or the Forge versions, and have launched the game at least once.
Great, now Forge is working. We can move on to installing the mods.
.minecraftfolder, on Windows you can type %appdata% in the Run dialog to find it.
Xaeros_Minimap_*_Forge_*.jarfile in the mods folder.
That's it! You should now have a working minimap installed.
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.