Find an Elytra in an End Ship
Equip the Elytra in your chestplate slot
Get fireworks rockets for boosting
Jump from a high place or use a launch point
Press the jump key while falling to start gliding
Steer with your movement keys and mouse
Use fireworks rockets to gain speed and altitude
Avoid crashing into the ground or walls
Repair the Elytra with phantom membranes or an anvil
Use a chestplate only when not flying with the Elytra