As Rod mentioned, Google can often be your greatest resource. I remember when I was new and didn't understand some functions on the PIL I just googled them and could spend alot of time to understand them, I still find myself searching some up if I'm unsure about the arguments to put in etc. But what helped me most after I read through the PIL was simply reading through other peoples code to get a better understanding of things.
I understand that most people that are new to the forums want to create a OS, but if they want to create a notable OS they should be pretty familiar with Lua and know how to use the more advanced stuff in it. ( coroutines for example ), they should also have more of a plan on, what's useful? how should it look? what can I do to make it unique? how do I want it?
These are some basic questions you should ask yourself before jumping in to create an OS, you should also take your time to create it, there's no need to rush it.
Just take a look at oeed's OneOS, he took his time to create that masterpiece and it's very unique. I would also like to add that multitasking would be one of the most important things in a great OS, if it can't do that then it'd just feel like a program with some GUI.
Here's a list of some Operative Systems with multitasking that I know of:
Now if you take a look at them, they're quite unique from eachother, which makes them more fun to try out. Now there's more Operative Systems than just those who're awesome, but I'm not usually testing out that many, these are just some I've personally tested.
If you want to learn more about multitasking then I'd suggest you'd check out
this tutorial by ChallengeMe( but I'd recommend that you learn the basics of Lua first )
