$dsn = 'mysql:host=localhost;dbname=prpr';
$pdo = new PDO($dsn , 'root', '');
$title = $_POST['title'];
$txt = $_POST['txt'];
$sel = $_POST['sel'];
$sql = "INSERT INTO forum(title,txt,sel) VALUES(:title,:txt,:sel)";
$query = $pdo->prepare($sql);
$query->execute(['title' => $title, 'txt' => $txt, 'sel' => $sel]);