A session is a way to store information(in variables) to be used across multiple pages.Unlike a cookie, the information is not stored on the users computer.Session variables hold information about one single user, and are available to all pages in one application.
Session variables are set with the PHP global variable: $_SESSION
<!- start a PHP session -->
<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>
<?php
$_SESSION["favcolor"] = "green";
$_SESSION["favanimal"] = "cat";
echo "Session var are set";
?>
</body>
</html>
<!-- get PHP session variable values -->
<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>
<?php
echo "Favorite color is" .$_SESSION["favcolor"]. ".<br>";
echo "Favorite animal is" .$_SESSION["favanimal"]. ".";
?>
</body>
</html>
<!-- show all the session variable values -->
<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>
<?php
print_r($_SESSION);
?>
</body>
</html>
<!-- modify PHP session variable -->
<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>
<?php
$_SESSION["favcolor"] = "yellow";
print_r($_SESSION);
?>
</body>
</html>
<?php
// remove all session variables
session_unset();
// destory the session
session_destroy();
?>
</body>
</html>
原文：http://www.cnblogs.com/forerver-elf/p/5212076.html