Grab a lift to the top of the castle, get on it, head to the flight trainer and fly to Dalaran for two gold. Most of my work is made for/on my DeviantArt page here: (The loading screen is from the video, from WoW of course). And Pepega Blizzard has some explaining to do.
Finally, hand in this quest, and you’re finished, you have Argus unlocked. Now, skip the cutscene, and you should be in Argus. Once you got onto the Vindicaar, hand that quest in and pick up the next quest. Once in Dalaran, go back to Khadgar, and pick up his quest, called “The Hand of Fate” and follow this quest line until you reach the Vindicaar. Hand this quest in, then go back to Dalaran.
After you’ve done that, you should appear on Broken Shore. Now, fly over to Krasus’ Landing, near the flight master, and pick up the quest “Armies of Legionfall”. Next, go to Khadgar, and pick up the quest “Uniting The Isles”, then hand it in to Khadgar. To get to Argus, first you’ll need to accept, the Pepega that is Blizzard.