"Psycho the movie"-help me understand?

Ok, I have seen the Psycho movies with Anthony Hopkins in it, but never could understand the movie. I remember the one with Jennifer Tilly in it that was made in the 80's. Is it about a son that is obsessed with his mother? Was Norman the one who killed all those people and watching from the window? At the end when he meets this old lady and talks to her in the kitchen, he hits her on the head with a shovel. Help me understand this movie. Thank you for everybody who answers