Jump on the gryphon (that's what they're called, those "flying things"), fly out to the fields and look for people running around among the undead. You need to look for those with a Fear icon over their head. Fly down close to them and use the action which calls them to you. If you remain still, they'll run towards you and jump onto your gryphon.
Fly back to Wintergarde and click the button which dismounts them (not you). Repeat until quest is done.
This is the Druid forum, by the way. You might have more luck getting additional information if you post in the
General WoW forum.