Something charming is usually pleasing or delightful. More rarely, it can be something supernatural.
Charms are magical objects and something charming puts you under its spell. In most cases, we mean that only figuratively — if you spent a charming evening with friends, it means their company was so wonderful it was almost enchanting. Charming people have a special, almost magical way of making others like them. But if you're talking about a charming witch, you better watch out for her sorcery and magic tricks.