- 15 minute overview of Lua: http://tylerneylon.com/a/learn-lua/
Lua language reference on just 2 pages: http://lua-users.org/files/wiki_insecure/users/thomasl/luarefv51.pdf
If a video is more your thing, here's an hour long beginner's guide to Lua: https://www.youtube.com/watch?v=S4eNl1rA1Ns
Beware that not all Lua modules have been ported to nodeMCU. As has been noted elsewhere, nodeMCU is actually based on eLua (http://www.eluaproject.net) and lacks certain modules:
- no IO module ( too much ram usage)
no OS module
no MATH module
no debug module
There are APIs specific to nodeMCU posted at: https://github.com/nodemcu/nodemcu-firmware/wiki/nodemcu_api_en