This main quest involves completing 3 sub quests, in any order:
To repay Thrall's hospitality, you have offered your services to the warchief. Fortunately, there is plenty of work for someone with your talents. Talk to Nazgrel, Drek'thar, and Gazlowe and help them complete their tasks.
You will find Drek'thar next to the Voodoo Lounge, west of Thrall's location.
Nazgrel is slightly south of Thrall, next to the barracks.
Gazlowe is in the farthest south east corner of Orgrimmar, next to the armory.