Garrisons will be phased outposts that players will establish in any zone on Draenor and use as headquarters for their adventures there. A garrison is basically a small town that can be upgraded and customized, but it has a functional aspect as well. Players meet NPCs during questing that will go back to the garrison where they can be put to work doing missions whether you're logged in or not. The garrison is integrated into the game world and can be visited by one's friends.
Different buildings in the garrison bestow different bonuses, such as an infirmary healing followers and inns allowing for greater recruiting. Buildings can be upgraded three times with a specialization choice at the end, and they can be decorated with monuments and trophies from achievement rewards (among other sources). Crafting, even in professions that you haven't trained, will be available, and Blizzard is promising that epic-quality gear can be made through this system.