If you have the Xbox One version, you can find an elytra in the tutorial world, then upload the save to the new version.
If you're starting fresh, an elytra is a set of wings that enables you to fly. You can find them in end cities. After you kill the dragon, you have to throw an ender pearl through a small floating bedrock portal that appears in the air near an obsidian tower. Once through, look for a floating ship up near the main end city structure. The elytra is in there.
This achievement is not as difficult as it sounds. First, dig a 1x1 hole that is at least 20 blocks deep. Then tunnel out and get back up to the surface. Next to the hole, build a tower that is at least 3 stacks of blocks high (just to be safe). Equip the elytra and jump off the tower, hugging the wall as you fall into the hole. As soon as you enter the hole, start tapping the jump button to activate the elytra. Unless there is water at the bottom or you are holding a Totem of Undying, you will die from this fall. However, this will get you the achievement.