$_GET
Pass the data in the form of url page.php?variable=value and read the values as `echo $_GET['variable']
$_POST
Pass the data using <form method="POST">...</form> and read the values as echo $_POST['variable']
$_SESSION
Start the session session_start();
Declare a variable $_SESSION['variable'] = "value";
Read the value echo $_SESSION['variable'];
$_SERVER
Declare a variable $_SERVER['variable'] = "value