Depends how you learn I guess, whether by example, book, experimenting, etc.
To be clear, LUA is a scripting language that Garry adopted for Garry's Mod.
Garry's Mod is a horrible resource to learn proper coding methods in my opinion as most of the code is not properly documented and it doesn't always perform as expected... Garry's Mod is unreliable and frustrating to debug sometimes. Also, Garry implemented C-style syntax that appear in some of the documentation that is not compatible with official lua.
However, it does have an advantage being that you have interest in manipulating the game play and that it might propel you to learn.
I would suggest checking this out ( http://lua-users.org/wiki/LearningLua (http://lua-users.org/wiki/LearningLua) ), building a foundation, and then going back to Garry's Mod.
http://www.lua.org/demo.html (http://www.lua.org/demo.html) --can use this to test your lua code during tutorials and shiz or can get binaries from here http://lua-users.org/wiki/LuaBinaries (http://lua-users.org/wiki/LuaBinaries)
http://lua-users.org/wiki/TutorialDirectory (http://lua-users.org/wiki/TutorialDirectory) --check out the tutorials here
http://lua-users.org/wiki/SampleCode (http://lua-users.org/wiki/SampleCode) --and here's some sample code you can play with and understand
I think this will give you a better understanding on how to approach the code.
Personally I think that understanding the syntax or structure is most important because you can take it and apply to other languages in the future noting the commonalities... I think it becomes much easier with more experience.