Try this experiment:
First, create a php file called page1.php with:
<?php
$msg='Grade A+';
?>
<a href="page2.php?msg=<?php echo urlencode($msg);?>">send message to page2</a>
, then create a second one called page2.php with:
<?php
echo $_GET['msg'];
?>
Start the Apache, launch page1.php on the browser and see the outcome.