Wouldn't say Lua is the easiest language to learn. It all depends on the developer though.
Have you read
this article about the Lua fundamentals on the Gmod wiki? If you're more of a visual learner, see if you can find some video tutorials on basic Lua.
You can learn a lot about a language just by experimenting with it. There's a bunch of code examples on the Gmod wiki you can play with.
Since you said you already know the basics, I encourage you to write some simple addons using the things you've learned so far. Use the Garry's Mod Wiki as a reference.
Here are some ideas:
- Console command that prints the nicknames of all players
- Kill every player that uses the words "kill", "dead" or "death" in a sentence
- Ulx command that tells you if any of your friends are also playing on that server
- ... (follow your curiosity)
Edit: Looking at your posts, I can see that's what you're already doing. Learning a programming language takes time. Experiment and play with them.