<form action="connect.php" method="post">
<label for="fname">Имя</label>
<input type="text" id="fname" name="first_name" placeholder="Имя..">
<label for="lname">Фамилия</label>
<input type="text" id="last_name" name="last_name" placeholder="Фамилия..">
<label for="lname">Почта</label>
<input type="text" id="email" name="email" placeholder="Почта..">
<label for="lname">Книги</label>
<input type="text" id="books" name="books" placeholder="Книги..">
<label for="lname">Срок книги</label>
<input type="text" id="term" name="term" placeholder="Напишите срок..">
<label for="country">Проживание</label>
<select id="country" name="country">
<option value="australia">Россия</option>
<option value="canada">Алматы</option>
<option value="usa">Казахстан</option>
</select>
<label for="subject">Описание</label>
<textarea id="subject" name="subject" placeholder="Напишите что-то.."
style="height:170px"></textarea>
<input type="submit" value="Отправить" name='sendFrom'>
</form>
if(isset($_GET['sendForm'])){
$first_name = $_POST['first_name'];
$last_name = $_POST['last_name'];
$email = $_POST['email'];
$books = $_POST['books'];
$term = $_POST['term'];
$country = $_POST['country'];
$subject = $_POST['subject'];
$host = 'localhost';
$username = 'root';
$password = '';
$db_name = 'library_db';
$connection = mysqli_connect($host, $username, $password, $db_name);
if (!$connection) {
echo 'Не могу соединиться с БД. Код ошибки: ' . mysqli_connect_errno() . ', ошибка: ' . mysqli_connect_error();
exit;
}
$nameSql = '"'.$mysqli->real_escape_string($first_name).'"';
$surnameSql = '"'.$mysqli->real_escape_string($last_name).'"';
$emailSql = '"'.$mysqli->real_escape_string($emailSql).'"';
$booksSql = '"'.$mysqli->real_escape_string($booksSql).'"';
$termSql = '"'.$mysqli->real_escape_string($termSql).'"';
$countrySql = '"'.$mysqli->real_escape_string($country).'"';
$subjectSql = '"'.$mysqli->real_escape_string($subject).'"';
$query = "INSERT INTO `users` (`first_name`, `last_name`, `email`, `books`, `term`, `country`, `subject`) VALUES (`{$nameSql}`, `{$surnameSql}`, `{$emailSql}`, `{$booksSql}`, `{$termSql}`, `{$countrySql}`, `{$subjectSql}`)";
$result = $connection->prepare($query);
$result->bind_param($nameSql, $surnameSql, $emailSql, $booksSql, $termSql, $countrySql, $subjectSql);
$result->execute();
if(mysqli_query($connection, $result)){
echo "Запись добавлена!";
}
mysqli_close($connection);
Только не ругайтесь :D