The Wiki

The wiki is going to be hands down the most useful thing to you in your gmod coding journey.
You may think I'm over exaggerating, but I'm not even one bit.
So, the wiki link is Let's go there shall we?
Alright so the first thing you'll see is the landing page.. It may look a bit crazy but hold up.
Let's take a look at it step by step and what it's best uses are.

The Search Bar

Now the search bar you're going to use A LOT, like a lot a lot.. If you take a look at the page, it *should* be here:

If the search bar isn't there.. uhm, I don't know what to tell ya.
Anyhow, in the search bar you search for things that you want to learn to use..
So like, let's say we want to learn about the player, we type Player in there.
As you type it will pull up options for you to choose, like so:

This pulls up search results with the world Player in them as well as Player functions and things we can touch.
Let's click on GM:AllowPlayerPickup

Let's break it down:
The pink arrow refers to the function (learned next) and it's parameters (next as well). We'll go over this more later as well as the square and its colour meaning.
The aqua arrow refers to what it does. In this case, GM:AllowPlayerPickup is used when a player tries to pick up something using their use key, aka E.
The dark blue arrow refers to the arguments, aka parameters. This will be explained later on. But in this case, this function takes 2 things, it needs a player and an entity. Again, this will be explained later.
The yellow arrow refers to what the function returns. This, again, will be explained later on. This one returns whether or not the player can pick up the item.
Below all that is the examples, this is just code so that you can see how it works.

This is honestly mostly what you'll use.. the search bar. That's it. You're free to explore the wiki if you'd like..

But when you're ready, click me