Fixed

For create.php

<?PHP

$db_host = "localhost";
$db_user = "root";
$db_pswd = null;
$db = "wizguin";
$username = $_POST['username'];
$password = $_POST['password'];

$conn = @mysqli_connect($db_host, $db_user, $db_pswd);

if(!$conn) {
    die("Failed to connect: " . @mysqli_connect_error());
}

echo "Connection was successful";
@mysqli_select_db($db);
echo "Selected database: " . $db;
@mysqli_query("
SELECT `users` FROM 1,
INSERT INTO `users`(`id`, `username`, `password`) VALUES(AUTO_INCREMEMT, " . $username . ", " . md5($password) . ");");
echo "Query is " . @mysqli_stat();

?>

For register.php or register.html

<form method="post" action="create.php">
<input type="text" id="username" value="Username"/>
<input type="password" id="password" value="Password"/>
<input type="submit" onClick="create()" value="Register"/>
</form>