Take your standard compass into your hand and USE it to swap between Settings. Each setting can feature different needles, pointing at awesome things like diamonds, Strongholds, the nearest Mob Spawner ...
If the server you are on has it enabled, it might be an Item you have to craft first. The recipe is a compass in middle, with diamonds at the sides (left, right, top, bottom).
Short tutorial, FML VERSION:
I reserve the liberty of not responding to posts stating ("It crashes", "doesn't work") and so on unless you provide an error message or log. Read the included textfile.
All Downloads moved to my homepage for user convenience:
You can add your own searchable materials and needle colors.
Read the config file in .minecraft/config/ for more information and examples.
My other mods: