How to activate a form

Html form in file form.html:

<form action="send.php" method="post">
<input type="text" name="name" placeholder="First name" />
<input type="text" name="phone" placeholder="Phone" />
<input type="text" name="email" placeholder="E-mail" />
<input type="submit" value="Send" />
</form>

php script in file send.php:

<?php
$admin_email='';

$subject='New message';
if(isset($_POST['phone']) AND !empty($admin_email)){
$firstname='';
$phone='';
$email='';
$message=$firstname.$phone.$email;
$site_email= 'info@'.$_SERVER['SERVER_NAME'];
if($_POST['name'])$firstname='Name: '.$_POST['name'].$PHP_EOL;
if($_POST['phone'])$phone='Phone: '.$_POST['phone'].$PHP_EOL;
if($_POST['email'])$email='E-mail: '.$_POST['email'].$PHP_EOL;

$header = 'MIME-Version: 1.0' . "\n" . 'Content-type: text/plain; charset=UTF-8' . "\n" . 'From: '.$site_email.' <' . $site_email . ">\n";
mail(trim($admin_email), '=?UTF-8?B?'.base64_encode($subject).'?=', $message, $header);
echo 'Thanks!';
}

?>

sample: http://wordpress-expert.net/demo/php...orm/script.zip

It's easy to find a php code snippet that will process your form input, however, there are some security issues you should consider before you try to deploy any back-end code.