How to summon Bloody Mary?

I seen The Legend Of Bloody Mary and I am very interested in it. Do I walk into a bathroom and then turn off the lights or can I leave them on and the door open. And when I write my friends' names on the mirror with lipstick or fake blood, I heard that she comes for them too. Is that true that she comes for them. My sister Jasmine is possessed by a demon and if I write her name on the mirror then Mary Worth might come for her and try to kill her and then the demon would die. No priests live in my city or town.