[Haskell-beginners] State monad

Many of the tutorials on the state monad seem to suggest that you can use State as a data constructor, but I can't get this to work. E.g. in ghci after :m Control.Monad.State I can let f = (\x -> (x,x)) let y = state f but if I, let z = State f I get an error message: Not in scope: data constructor `State'. Can someone please explain? Thanks, Britt