I can give you an example a little more about its use in your mind about it. For example, by placing similar types of data in a single variable, you can access all the data you need with a single variable:

$message['title'] = 'Hello World!';
$message['content'] = 'Greetings, this is just an example to better understand arrays in PHP';
$message['author'] = 'Baransel';
$message['date'] = 'Thursday, December 23, 2010';

As you can see, I just kept all the data of a message in a regular and separate way with only the $message variable.