register_sidebar

I’m looking at this code from a sample on how to build an accordion menu. I am supposed to include this into my functions.php file. I think what it is doing is checking to see if the function register_sidebar exists and sending an array as a parameter. More importantly could someone elaborate on what the function is actually doing? I don’t understand this just yet.

<?php
    if(function_exists('register_sidebar')){
        register_sidebar(array('name' => 'appleQuery'));
    }
?>