<?php
$host = "localhost";//Your mysql host name
$user = "root";  //Username to access the database;
$pass = "password";//Password to access the database;
$db = "_db_name";//The database where you created the tables
?>

<?php
mysql_connect(  $host, $user, $pass  ) or die( mysql_error() );
mysql_select_db(  $db );
?>

CREATE TABLE tbl_auth_user (
user_id VARCHAR(10) NOT NULL,
user_password CHAR(32) NOT NULL,

PRIMARY KEY (user_id)
);

INSERT INTO tbl_auth_user (user_id, user_password) VALUES ('theadmin', PASSWORD('chumbawamba'));
INSERT INTO tbl_auth_user (user_id, user_password) VALUES ('webmaster', PASSWORD('webmistress'));


//Now that that is created I looked at the PHP code and this is what I have questions on.

<?php
// we must never forget to start the session
session_start();

$errorMessage = '';
if (isset($_POST['txtUserId']) && isset($_POST['txtPassword'])) {
   include 'library/config.php';
   include 'library/opendb.php';

   $userId = $_POST['txtUserId'];
   $password = $_POST['txtPassword'];

   // check if the user id and password combination exist in database
   $sql = "SELECT user_id
           FROM tbl_auth_user
           WHERE user_id = '$userId'
                 AND user_password = PASSWORD('$password')";

   $result = mysql_query($sql)
             or die('Query failed. ' . mysql_error());

   if (mysql_num_rows($result) == 1) {
      // the user id and password match,
      // set the session
      $_SESSION['db_is_logged_in'] = true;

      // after login we move to the main page
      header('Location: main.php');
      exit;
   } else {
      $errorMessage = 'Sorry, wrong user id / password';
   }

   include 'library/closedb.php';
}
?>