Assuming you read the basic Lua stuff from lua.org.
All other stuff comes from the Renoise.Song.API.lua.
The functions are not chewed out for you, but they are described in that document (assuming you have that and read it).
You can also download one of the many tools on the tools site that does specific things with patterns and instruments and explore the Lua code inside those tools and fork out routines that you think you can use.