save torch code

Hi, I am new to torch, I am looking ways to save the code written in torch in linux shell,
i found there are ways to save code by .th, .net and .dat,
Can anybody explain me these file extensions and how I can save the whole code from " require 'nn'" to training dataset.

Thanks in aniticipation

You can write a lua file, then run "th filename.lua" in your shell