===INDEX PAGE===
<?php
session_start();
$no_phpBB = true;
$pagetitle = "test";
require_once("../includes/head.inc");

if(isset($_GET['sessVar'])) {
        $_SESSION['sessVar'] = $_GET['sessVar'];
        echo "Session saved as".$_SESSION['sessVar'].". Now goto <a href=\"page2.php\">Page 2</a>";
}
echo "<br /><br /><form method=\"get\" action=\"index.php\"> <br /><br />
Variable: <input type=\"text\" name=\"sessVar\" /><input type=\"submit\" value=\"Save variable\" />";
require_once("../includes/foot.inc");
?>

===PAGE 2===
<?php
session_start();
$no_phpBB = true;
require_once("../includes/head.inc");
echo "The variable is: <b>".$_SESSION['sesVar']."</b>";
require_once("../includes/foot.inc");
?>