Overview

1. Create functions
2. Call functions
3. Anything else I can think of

Part 1: Creating a function

function DisplayAMessage takes string message returns nothing
    call DisplayTextToPlayer(Player(0), 0, 0, message)
endfunction

Now, the word 'function' tells the program that you will be declaring a function. The next part of the function is the name of the function. You need to make sure your function has a unique name that no other function has, otherwise you'll get errors when saving a map. Next, you tell the program what the function 'takes' or needs pretty much. This function 'takes' a string, which is basically a message of some sort. After you put the type the function needs, you then have to put a name for it (so you can refer to it inside of your function). Lastly, you tell the program the type the function will return. You could make this a string, integer, real, and so on. However for this example, no value will be returned so we put 'nothing'.

After declaring a function, inside the function you need to put what the function does, otherwise it would be pretty useless. This function simply calls another function using the string value that is needed to call it. Lastly, you need to tell the program when the function ends, you do this by putting 'endfunction' at the end of the function.

Part 2: Calling functions

call DisplayAMessage("hello")

This line would call the function I just showed you. When calling a function this way, you need to have the word 'call' followed by the function name which is then followed by parenthesis with the values the function takes inside of them. If a function takes multiple values, they are each separated by a comma ',' like in the DisplayTextToPlayer function. It works that same way when declaring functions too (whoops forgot to mention that earlier)

Now, I will go over what the return values in functions are. They're pretty simple really, though I don't want anyone to be confused about anything. When a function has a return value, you can set variables that are the same type as the return value to that function. Here's an example:

Code:
local string player_name = GetPlayerName(Player(0))

Now, see that when you set a variable to the return value of a function, you don't need the word 'call'. Also, if you want to pass the return value of a function, you don't need to put the word 'call' either, as seen with the Player function that was the needed parameter in the GetPlayerName function. Also, and this is important when declaring a function, if the function declaration states that the function returns a value, somewhere in the function if must have a line that 'returns' the value, like so:

Code:
function TestReturn takes nothing returns integer return 5 endfunction

There is one last thing you need to know when calling functions, you can only call a function that is above another, since that may not make complete sense, here's an example:

Code:
function SomeFunction takes nothing returns nothing endfunction function SomeOtherFunction takes nothing returns nothing endfunction

Now, this is only used as a visual example so I can more easily describe what I was saying. You can only call a function that is above the function you are currently in. So, 'SomeOtherFunction' would be able to call 'SomeFunction'. However, 'SomeFunction' wouldn't be able to call 'SomeOtherFunction'.

Challenge Time!

function Function2 takes nothing returns string
 local string message = SomeFunction("Hello World")
endfunction

function SomeFunction takes string returns nothing
 local string a message
    a message = 'Something is wrong'
    call DisplayTextToPlayer(Player(0), 0, 0, a message)
endfunction