[Haskell-beginners] how to input a Let expression

Hi, I'm missing something basic here, I wrote this program a while back. But I cant remember how to work it. Would someone please explain how I enter a value for a variable x,y etc and get this to work. It goes by entering evaluate [][test1]test1 but I cant remember how to write in The Let part and not have it keep ending in -no definotion of a variable. John