If you have any programming experience at all (even HTML or something) I'd suggest finding a simple addon that does one thing (maybe something similar to what you want to do), and read through its code. Lua is a very "human readable" language.
Use lua.org to look up Lua functions/syntax, and wowwiki.com to look up WoW API functions. Ask questions if you can't figure out what a particular section does.
There are a few "get started" tutorials floating around but honestly, I never found that kind of thing helpful. I learn much more quickly and thoroughly by referring to working examples, rather than "hello world".