Moongates allow players to travel across vast areas instantly. If you come upon a Moongate, it is always wise to click on it first to investigate where it might lead. Shown in the image below is a Town Gate as an example.
There are several types of gates here on Outlands, such as:
Town Gates - Located outside of every township, these gates remain open constantly providing ease of travel to all townships as well as The Arena
Player Gates - These gates are cast by players so be careful entering them if you do not know the player or destination
Dungeon Gates - Found scattered throughout the dungeons of Outlands, these gates are effectively 'exit' gates only, for expediting your return to town from within the dungeon
Event Gates - These gates, when open (typically at banks), will bring players to shard events that are currently underway
Death Gates - Seen ONLY by ghosts (dead players) these gates are scattered throughout dungeons much more than Dungeon Gates, potentially saving time when trying to recover your body's contents
There may be more gate types unlisted or added in the future. Always gate safely and click for details before passing through.