"You have to wait until you have unlocked this ability to get this trophy. To use this hold after jumping. This should come fairly quickly but if you want a few good places to fly from, the best place would be to climb the tower that you dropped the food from at the start of the story and fly off there or the tower from your fight with Alden. Of course, you could get this from flying off of any building, even if you simply jump into the air and fly down. You should really just play the game and wait for this to unlock naturally."