The Garrison is a new feature introduced in World of Warcraft: Warlords of Draenor, much akin to Player Housing than one might think, yet with striking differences.
There is no capital city in this expansion such as Shattrath City (in Burning Crusade) or Dalaran City (in Wrath of the Lich King). The Garrison is your to-go place of operations. You might want to go there every 30-60 minutes.
The Garrison is your foothold on this savage-savage land, and you have few resources and few soldiers among your troops to call upon, without reinforcements coming from the Dark Portal. By the way, all NPCs including High Overlord Saurfang address you as Commander of this expedition.
It is in the Garrison where you can expand your buildings, their specialization, and even where you can hire new NPCs to fight for you or to accomplish special tasks. In this guide I’ll only cover the buildings and their upgrades.