como buscar dados do banco de dados mysql usando php

$headers = 'From: [email protected]' . "\r\n";
$mysqli = new mysqli("localhost", "user", "password", "database");
$output = $mysqli->prepare("SELECT id FROM table WHERE x=?");
$output->bind_param("s", $parameter);
$output->execute();
$output->store_result();
$output->bind_result($id);
while ($output->fetch()) 
{
    mail($to, $subject, $emailcontent, $additionalheader);
}
$output->close();