I have a few stories about spirits at my grandma's house, only me and her have ever got a first hand experience from it

ANYWAY, she went to go see this psychic lady and she knew everything about her Dad and she said he was with us when we were together as a family, she knew how he died, when he died, his name. She knew the mom and son took it badly.

HOW DO THESE PEOPLE WORK? Please someone shed some light on psychics, my grandma rang up from a payphone (ex cop grandad told her to)