It's psychosomatic hypnosis shit, nigga. Let me show you the power of suggestion. Get a friend implying you have irl friends, have them hold a string with a weight on the end, and repeatedly tell them that you are going to spin the weight in a circle with your mind. Over and over just repeat that the weight will soon begin spinning clockwise because you are focusing psychic energy on it, and to your and his surprise, it actually will. Not because you did anything psycic, but because your friend unconsciously began spinning the weight thanks to hypnosis. He won't notice his wrist moving though you might, because the length of the string allows very subtle movements to have every large impacts.
Ouija boards work exactly the same way. That's why they "work best" when multiple people are holding the magic stone or whatever simultaneously. If enough people stand around holding the stone and calling out to spirits, eventually one of them will succumb to group suggestion and push/pull the stone in a particular direction. Everyone else will think the spirits are trying to say something, and unconsciously try to "assist" them by moving the stone wherever they think it should go, and so on and so forth, while the number of people holding the stone will mask and muddle the identity of whoever gave the initial push, making everyone think a ghost did it.