Art - Darnassus is confusing. To exit darnassus, there's a exit west of the bank in the middle.

After exiting Darnassus, there is a boat at Rutheran Village. If you want to go to stormwind, there should also be a boat that takes you to stormwind.

Or alternatively, the griffins outside should take you to Feralas on the mainland. That's the sequence of quests if you are questing from the Elven side.

Hope that helps