when you create a torrent you use the standard announce (it shud tell you on the upload page of your site and will look like
http://www.domain.com/announce.php)
when you have uploaded the torrent the next thing you do is download it to start seeding .. when you click the download link it sends you to download.php where the torrent file is edited, recompiled and sent to you.. during this time the script selects your passkey from the users table (if a passkey is not there it will generate one for you, insert it into the users table for future use and then use that passkey) and then it edits the tracker url string to
www.domain.com/announce.php?passkey=xxxxxxxxxxx where passkey is the one it selected from the users table