About haskell, how to define function in file?

I am totally newbie to haskell.

I have such snippet code

lucky:: Int->String
 lucky 7 = "LUCKY NUMBER SEVEN!"
 lucky x = "Sorry , youre out of luck pal!" 
 

I tried to input to terminal directly, seems not right.
But if I want to put this in file and load this file, then call lucky function. How should I construct this file?
Thank you!

I tried this:

module Main where
 lucky:: Int->String
 lucky 7 = "LUCKY NUMBER SEVEN!"
 lucky x = "Sorry , youre out of luck pal!" 
 
 
 main = do 
 

But when i try to call lucky in terminal, i got this:

factorial.hs:7:8: Empty 'do' construct
 lucky 7
 
 <interactive>:1:1: Not in scope: `lucky'
 

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