Instructions
Right click on the notice board located in your faction's capital city. Horde players should visit the Warchief's Command Board near the Orgrimmar auction house, while Alliance players should examine the Hero's Call Board between the bank and auction house in the trade district of Stormwind City.
Click on the "To Vashj'ir!" option in the notice board's pop-up menu to accept the introductory Vashj'ir quest.
Press "L" to open a list of your active quests and click on "To Vashj'ir!" to view the quest objectives. Speak to the nonplayer character (NPC) specified in your quest objectives to complete the quest. Horde players must speak to Commander Thorak in the nearby Bladefist Bay. Alliance characters must speak with Recruiter Burns at Stormwind Harbor.
Right click on Commander Thorak or Recruiter Burns after completing the "To Vashj'ir" quest. Click on the quest titled "Call of Duty" in the dialogue window to accept it. Proceed to the docking area of your faction's capital, as the quest instructions indicate.
Board the ship to Vashj'ir in Orgrimmar's Bladefist Bay or Stormwind City's Stormwind Harbor and wait for its departure. After a lengthy cut scene in which your ship sinks, your character emerges amid the ship wreckage at the starting quest hub for the Vashj'ir zone.