It seems somebody has to say this on every single ‘Lua Help’ thread these days.
Right, Garry’s Mod utilises the scripting language Lua and adds a API for you, the developer, to interact with the game. It is virtually impossible to effectively code for Garry’s Mod if you are not already fully comfortable with programming concepts and their use in Lua.
Firstly, I suggest you look into learning how to code before jumping into Garry’s Mod. I have come across a shocking amount of people who have developed a wide range of bad habits and misconceptions from learning to code directly in Garry’s Mod. Once you know how to code and develop the mind-set for it all; you should then jump into learning the Garry’s Mod API :3
(Also for those who know more than me, am I right in referring to the Garry’s Mod ‘API’ as an API? It doesn’t seem like it suits.)