Lua doesn't let you use mods, it lets you use scripts.
Scripts are easier to modify, enable/disable and can be used on any powder toy version,
while in mods you can code more mechanisms but you cant open saves from more recent versions.
Just put the autorun.lua from https://powdertoy.co.uk/Discussions/Thread/View.html?Thread=19400
into the folder where you have powder toy, then put scripts in a folder that is created called "Scripts".