cookies code

Hello im creating a script that uses the punnbb cookies and login system

I start the file with this:
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<?php
$pun_root = './';
require './include/common.php';
require './header.php';
?>
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And end it with
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<?php
require './footer.php';
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No i want to use if and else statements that use the cookie.

if
(cookie says that users is a guest)
echo "Please login to use this section"

else

all the scripts code
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Can you guys tell me where i can find this cookie information or how to what the code is?