i think at first you should become familiar with lua itself. try to google some tutorials, hello world and so on...
http://www.lua.org/download.html
thats the page to start. download lua. scite is included and a nice editor as far as i can see. i have tested 2 others (textadapt and luaIDE 2010) and they were both crap/early stage.
in scite dont forget to name your file .lua. else debug/run/compile wont work.
http://www.lua.org/manual/5.1/
there you will find the manual for lua. i dont particularly like the syntax but it propably has its strengths as every scripting language.