What happens if someone got alzheimer;s disease, does it cause your brain not functioning or does it kill the brain cells?

Yes.: The brain cells die causing neurofibrillary tangles with amyloid deposits that completely destroy the architecture of the brain and destroys the communicating system between the brain and the rest of the body hence they are confused, forgetful and agitated because everything is always new to them. In the latter stages, they can't feed themselves, lose function of bladder and bowel.