[Haskell-beginners] A newbie question

Hello All, Today I wrote my first Haskell program, which is module Main where f 1 = 1 f n = n*f(n-1) main = putStrLn (show (f 5)) After compilation, this program runs with no problem and gives 120 (which is correct). I have two questions though: 1. What does "where" in line 2 mean? Why I should put it here in this place? If there is no "where" here, the program cannot run. But what is the syntactical meaning of "where"? 2. Why this module can end without an "end" sentence? And what are the blank lines treated as? Thank you for your answer, well, in advance. These are newbie questions indeed. Best wishes, Mr. Zhou