The Stables is a large plot garrison building that can be built by Garrison Resources. The Stables enables the capture and training of special mounts on Draenor, Also allows you remain mounted while interacting with objects in outdoor Draenor zones.
Garrison Stables will will unlock to the next Level after completing the corresponding daily tasks. You can purchase the blueprint to upgrade to level 3 Stables when you earned six mounts, and then you can complete the last achievement The Stable Master and get a title and a wow mount.
Defeat all mount-in-training targets in Nagrand while carrying the Garn-Tooth Necklace. Kill them over and over on different mounts. Then The Stable Master will be completed.
It only needs to do some quests each day then you will get eight wow mounts and a title. Once done, the Stables could be replaced by other buildings.