I read the Halloween event post but i don't understand one thing, what can i do with halloween candies? and where can i use it?
They're for physical goods that only those that live in South Korea would be able to get. Don't worry about them.
Its for a raffle, and you must be living in korea, even if you win (something that isn't worth much) you will have to confirm your real life information as a korean citizen to claim the prize, so yeah you don't need them.
I don't include Korean-only event details on the event posts, that's why its not on the translated event page :/