To use Z-Moves in Pokémon Sun and Moon, you’ll need two Key Items – a Z-Ring and a Z-Crystal. There are two conditions for performing Z-Moves – a Pokémon must learn a move of the same type as a Z-Crystal and it must be holding the corresponding Z-Crystal. If you wanted to learn how to make your very own Ghostium Z, check out the video below:
How to make your very own Ghostium Z based on Pokémon Sun and Moon Z-Crystals
Pokémon Blog 