There are varying degrees of preparations to be safe for various mushrooms. There are a few you can eat raw. There are a few that will kill you even if you cook them 10 times. And there is everything in between - from mushrooms that you cook once, to those you need to cook 3 times, replacing the water each time and ventilating to not inhale the vapor :))

Source - 30 years of experience foraging and learning from grandmom.