What is the purpose of certain words between parenthesis

Below I have explained how the code works:

Let's start by looking at the print function:

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

print takes a string message as an argument and calls document.write(message). document.write writes a string to the browser, i.e., it is that call that shows the playlist in the browser. Therefore it doesn't work if you comment it out.

Now let's look at the printSongs function:

function printSongs( songs ) { 
    var listHTML = '<ol>'; 
    for ( var i = 0; i < songs.length; i += 1) { 
        listHTML += '<li>' + songs[i][0] + ' by ' + songs[i][1] +'</li>'; 
    } 
    listHTML += '</ol>'; 
    print(listHTML); }

This function takes an array songs, which it uses to create an HTML string, so line 1-5 inside the function just creates the HTML which represent the songs. Since we now have the HTML string containing information about the songs, we can call the print method (line 6 inside the function), which then displays the songs list in the browser. This is what happens since message in the print function now contains the HTML string saved in listHTML.

Now all we need is to call the function printSongs with the playList we would have shown in the browser:

printSongs(playList);

Just one point to add on top of the previous responses that a professor of mine used to really stress is that the names of the arguments passed in do not matter, only the order. Let me explain with an example:

if you have this function from the above answer:

function addNumbers(firstNumber, secondNumber){
  return firstNumber + secondNumber;
}

those two argument names only exist within the function. So when you call it, you can pass in whatever variables you want and it will assign them to those arguments in the same order. So if you have two variables like this:

var num1 = 5;
var num2 = 10;

You could call the function like so:

addNumbers(num1, num2);

And when the function runs, it's going to assign those variables to the arguments in the same order they're listed in the function. So firstNumber becomes num1, secondNumber becomes num2.

And if you reverse the order when you pass them in like this:

addNumbers(num2, num1);

It's still going to assign them in the order they're listed. So now firstNumber is num2, and secondNumber is num1.

all the answers above are really good! I just came to recommend the JavaScript Basics course. It explains a lot of things related to functions. Given that you didn't know what arguments are, perhaps there are still gaps in your knowledge about functions and you could benefit of watching the last section of the course I mentioned before continuing with this one. Good luck!