To set cookie : setcookie()
See http://www.php.net/manual/en/function.setcookie.php
To retrieve a cookie value : $_COOKIE["<cookie name>"]
Example :
On one page :
<?
SetCookie("user_logged_in", "1", time() + 3600); // Expires in one hour
// Rest of the code...
?>
On the other page :
<?
$cookie_value = $_COOKIE["user_logged_in"];
// Rest of the code...
?>
NOTE : You must call setcookie() before outputting anything... if you don't care about this, the cookie won't be set because headers are already sent and you cookie won't be set !