There are many great free online resources for Lua including:
- A highly recommended detailed and authoritative introduction to all aspects of Lua programming by Lua’s chief architect: Programming in Lua (2nd edition), by Roberto Ierusalimschy available online at www.lua.org/pil/
- For an official definition of the Lua language, consult the Lua 5.1 Reference Manual , by R. Ierusalimschy, L. H. de Figueiredo, W. Celes available online at www.lua.org/manual/5.1/
- Additional documentation is available at www.lua.org/docs.html
- A live, interactive demo of Lua is available at www.lua.org/demo.html. This is an excellent place to see some simple sample programs and to play with your own.
And really everything at lua.org.
Follow up with any others you know of.