I presume you have MySQL 3.22.x or higher and PHP 4 installed on your system.
Then open the configuration file 'config.inc.php' found in the admin directory with a text editor and set up your database settings.
<?php
/* database settings */
$GB_DB["dbName"] = "guestbook";
$GB_DB["host"] = "localhost";
$GB_DB["user"] = "Username for MySQL ";
$GB_DB["pass"] = "Password for MySQL";