This example show how to handle session. In this example I tried to focus on a single form that will self_post a html block that will be only displayed when the user is logged in with correct password.
<?
//start a session
session_start();

//check if user is coming from a form
if ($_POST[op] == "sos") {

//check username and password
if (($_POST[username] != "manas") || ($_POST[password] != "tuktuk123")) {

//handle bad login
$msg = "<P><font color=\"#FF0000 \"><strong>Could Not-- Login -Please Try Again</strong></font></P>";
$show_form = "yes";

} else {

//handle good login
$_SESSION[valid] = "yes";
$show_menu = "yes";
}

} else {

//determine what to show
if ($_SESSION[valid] == "yes") {
$show_menu = "yes";
} else {
$show_form = "yes";
}
}

//build form block
$form_block ="<h1>Login</h1>
<form method=POST action=\"$_SERVER[PHP_SELF]\">

$msg

<P><strong>username:</strong><br>
<input type=\"text\" name=\"username\" size=15 maxlength=25></P>

<P><strong>password:</strong><br>
<input type=\"password\" name=\"password\" size=15 maxlength=25></P>

<input type=\"hidden\" name=\"op\" value=\"sos\">

<P><input type=\"submit\" name=\"submit\" value=\"login\"></P>
</FORM>";

//build menu block
$menu_block ="<h3>Testing Area for session and mysql admin pages</h3>
<P><strong>Administration</strong>
<ul>
<li><a href=\"show_page1.php\">Page 1</a>
<li><a href=\"show_page2.php\">Page 2</a>
<li><a href=\"http://spiritofsoccer.com/Index_Files/right_Admin.html\" target=\"main\">Admin </a>
</ul>
<P><strong>View Recorsos</strong>
<ul>
<li><a href=\"show_contactsbyname.php\">Show Contacts, Ordered by Name</a>
</ul>";

//assign the block to show to the $display_block variable
if ($show_form == "yes") {
$display_block = $form_block;
} else if ($show_menu == "yes"){
$display_block = $menu_block;
}

?>
<HTML>
<HEAD>
<TITLE>Authentication with session</TITLE>
</HEAD>
<BODY>

<? echo "$display_block"; ?>

</BODY>
</HTML>
if your log in is correct
destroying the session

<?
//start a session
session_start();

//check if user is coming from a form
if ($_POST[op] == "sos") {
$url=='http://'.$_SERVER['HTTP_HOST'].dirname($_SERVER['PHP_SELF']);
//check username and password
if ((substr($url,-1)=='/')OR (substr($url,-1)=='\\')) { $url =substr($url,0,-1);}

$url.='auth_session_1.php';
header("Location:$url");
exit();

} else {

//handle good login
$_SESSION=array();
setcookie('PHPSOSID','', time()-300, '/','',0);
session_destroy();
}
echo " you are logged out";
?>
Please also cjech unset
 
 Please also check with unset function
<?php
session_start();
if(isset($_SESSION['views']))
$_SESSION['views'] = $_SESSION['views']+ 1;
else
$_SESSION['views'] = 1;

echo "views = ". $_SESSION['views'];
?>
 
<?php
session_start();
if(isset($_SESSION['cart']))
unset($_SESSION['cart']);
?>