A Key Stone must be unlocked and worn for a player to Mega Evolve a Pokémon. If a player wears a Key Stone, a Pokémon owned by the player will be able to Mega Evolve in battle if it is holding its corresponding Mega Stone. If the Key Stone has not been unlocked, or if the player has unlocked the Key Stone but is not wearing it, Mega Evolution cannot be used.
By defeating a Mega Evolved boss Pokémon, the player will unlock the option to equip a Key Stone. This will usually be in the form of a bracelet. Once this option is available, the player can wear and take off the Key Stone in the inventory screen. The Mega Bracelet will be visible on the player's left hand when it is worn.
For players who have boosted the discord server and have their discord account linked to their forums account, as well as having their forums account linked with their minecraft account via PixelLink, there will also be the option to wear it as a necklace. It will be visible around the player's neck.
The same way as obtaining the Mega Bracelet you can obtain the Mega Glasses, which works in the exact same way as the Mega Bracelet but it is visible in the player's face as sunglasses with the mega stone logo on its sides.