Equipping an Elytra

1. Open your inventory.
2. Locate the elytra slot beside your armor slots.
3. Place an elytra into that slot (drag-and-drop, or use the quick-equip action the same way you would for armor).
4. Put a chestplate in your normal chest armor slot for protection.

You now have armor and wings equipped together. To glide, jump from a high point and hold jump as usual; to stop using the wings, simply remove the elytra from the slot.