[The Scyphozoa]

Ah, yes. This option is disabled by default. You can enable it in UI Options.

On the full-screen map, it will place a ring directly on the location of an NPC you need to talk to. If there is a mob(s) you have to kill, the general area will be highlighted. On the minimap, an arrow with a ring around it points you to this area or NPC. When you are in the general area (in the highlighted area or withing radar distance of the NPC), the arrow disappears and the area name under the minimap glows.

I'm not entirely sure how the system for choosing which quest to show you on the minimap works, but I know that you can right-click the ring next to any quest and click "Set Quest Guide Focus", and the minimap will show the arrow for that one. On the full-screen map, there is a box (which gets in the way, you can drag it around but it doesn't stay put when you close and open the map again) with a list of all your quests. You can check and uncheck the quests in this box to choose which ones to mark on the map.

This does not work for all quests, does not work for deeds, and does not work in instances.