everything i know of uses 5.1, so it's probably good to start with that
i'd link the 5.1 ref. manual, but it's not really a good tutorial
you could probably find a really good tutorial for 5.1 on lua-users
...
yep, here's a list of pages that basically teach you about everything - variables, functions, conditions, etc.
http://lua-users.org/wiki/TutorialDirectoryand in case you need it, here is lua for windows:
https://code.google.com/p/luaforwindows/you can run the lua interpreter by just typing "lua" in the command prompt after installing this.