Step by step describing the script

Create the array playList with items.

var playList = [ 'I Did It My Way', 'Respect', 'Imagine', 'Born to Run', 'Louie Louie', 'Maybellene' ];

Your understanding is correct.

Create a message? Where does this come in? What does this do? A global scope?

function print(message) {
    document.write(message); 
}

That line of code creates a function called print. message is a parameter for the function, meaning that you can pass data into it when the function is called. Code within a function is not run until the function is called in the code. The message variable within the function will be set equal to whatever data is passed into the function when it is called.

The function itself simply calls document.write with the value that was passed into the function when it is called.

We create a function, but why do we put 'list' here? Is it a name? But isnt 'printList' the name?

function printList ( list ) {

printList is indeed the name of the function. list is the name of the parameter. Parameters are basically variables that are populated when the function is called. So list will be assigned whatever value is passed to the printList function when it is called. Values that are passed to a function is called an argument.

We create a var that creates our ordered list.

var listHTML = '<ol>';

It is a var that will end up containing the ordered list.

We create a for loop that changes the content(or parameter? What is the right term?) of 'listHTML' so that it now creates a list item to the ordered list. But what does the '[i]' mean? And how can we use 'list.lenght' here? How come 'list' is populatet? Shouldnt it be playList.lenght?

for ( var i = 0; i < list.length; i += 1) { 
    listHTML +='<li>' + list[i] + '</li>'; 
}

Content is the more appropriate right term. You can pull out data from a list by referencing the index of the data you want to pull out within square brackets. And indexed start at 0. So list[0] for example would pull out the first item of the list. list[1] would pull out the second item from the list and so on.

i is a variable that starts at 0 within the loop and is increased by one each time the loop runs. by using that as an index to pull from you end up pulling out the first item from the list the first loop, the second item in the second loop and so on. All of the items in the list ends up being pulled out before the loop ends.

list is already populated due to it being a parameter as I explained above, it will contain whatever argument is passed in to the function when it is called. Passing data into a function through a parameter makes it more flexible than having the function refer to data outside of it.

We again change the listHTML var to close the ordered list

listHTML += '</ol>';

Correct.

We print the function 'printList' to the page.

print(listHTML); }

Not quite. You call the function print and pass it the listHTML variable as an argument. Meaning that the message parameter within the print function will be set to the contents of listHTML when the code within it runs.

You didn't ask about the final line but I'll include an explanation for completeness:

printList(playList);

This line calls the printList function with playList as an argument. So list within the printList function will contain the content of playList.

This explanation was written somewhat quickly and I tried to be somewhat succinct since there were a lot of questions to go through. If you want more details on any of these points or found part of my explanation unclear then feel free to reply with follow up questions. I'll gladly answer any question that I can.