The commands you might need are:
The Lua functions:
http://www.wowwiki.com/Lua_functions
The WoW basic API:
http://www.wowwiki.com/World_of_Warcraft_API
The API of WoW's frames and such:
http://www.wowwiki.com/Widget_API
Also, you can get more on Lua than what is on wowwiki by checking
the user manual or
the users' wiki.
(One addition on the "string" part of Lua's functions by wowwiki is that the concatenation symbol is "..", as you might have already noticed)