You cannot craft an Elytra in Minecraft
Find an Elytra in the End Ship of an End City
Defeat the Ender Dragon to access the End islands
Travel to the outer End islands
Locate an End City
Find an End Ship attached to the End City
Take the Elytra from the item frame inside the End Ship
Repair the Elytra with Phantom Membranes or combine two Elytras on an Anvil