Below are the PHP5 SuperGlobals

• $GLOBALS
• $_REQUEST
• $_GET
• $_POST
• $_FILES
• $_SERVER
• $_ENV
• $_COOKIE
• $_SESSION

$GLOBALS: This SuperGlobal Variable is used for accessing globals variables.

<?php    
$a = 10;    
function foo(){
    echo $GLOBALS['a'];
}    
//Which will print 10 Global Variable a
?>

$_REQUEST: This SuperGlobal Variable is used to collect data submitted by a HTML Form.

<?php
if(isset($_REQUEST['user'])){
    echo $_REQUEST['user'];
}
//This will print value of HTML Field with name=user submitted using POST and/or GET MEthod
?>

$_GET: This SuperGlobal Variable is used to collect data submitted by HTML Form with get method.

<?php
if(isset($_GET['username'])){
    echo $_GET['username'];
}
//This will print value of HTML field with name username submitted using GET Method
?>

$_POST: This SuperGlobal Variable is used to collect data submitted by HTML Form with post method.

<?php
if(isset($_POST['username'])){
    echo $_POST['username'];
}
//This will print value of HTML field with name username submitted using POST Method
?>

$_FILES: This SuperGlobal Variable holds the information of uploaded files via HTTP Post method.

<?php
if($_FILES['picture']){
    echo "<pre>";
    print_r($_FILES['picture']);
    echo "</pre>";
}
/**
This will print details of the File with name picture uploaded via a form with method='post and with enctype='multipart/form-data'
Details includes Name of file, Type of File, temporary file location, error code(if any error occured while uploading the file) and size of file in Bytes.
Eg.

Array
(
    [picture] => Array
        (
            [0] => Array
                (
                    [name] => 400.png
                    [type] => image/png
                    [tmp_name] => /tmp/php5Wx0aJ
                    [error] => 0
                    [size] => 15726
                )
        )
)

*/
?>