PHP Onsubmit send email - php

Question

I have a form where a receptionist enters a visitors information, first name, email etc and I want to send an email to the visitor using their email address entered in the form.
I have the php mail function working however it currently only sends to a specific sender that I manually specify. How do I make the submit button on this form send an email based on the contents of the email field?
I assume I need to do something like this
<?php
$to = $row['email'];
$subject = 'Welcome ' . $row['first_name'] . ';
$message = 'You have been booked in';
$headers = 'From: noreply#blah.com' . "\r\n" .
'Reply-To: noreply#blah.com' . "\r\n" .
'X-Mailer: PHP/' . phpversion();
mail($to, $subject, $message, $headers);
?>
I dont think the $row[] is correct as I want to pull from the form, not the table that the form is inputting into.
This is the form page:
//serve POST method, After successful insert, redirect to customers.php page.
if ($_SERVER['REQUEST_METHOD'] == 'POST')
{
//Mass Insert Data. Keep "name" attribute in html form same as column name in mysql table.
$data_to_store = filter_input_array(INPUT_POST);
//Insert timestamp
$db = getDbInstance();
$last_id = $db->insert ('tb_bookings', $data_to_store);
if($last_id)
{
$_SESSION['success'] = "Visitor signed in successfully!";
header('location: bookings.php');
exit();
}
}
//We are using same form for adding and editing. This is a create form so declare $edit = false.
$edit = false;
require_once('includes/admin-header.php');
?>
<div id="page-wrapper">
<div class="row">
<div class="col-lg-12">
<h2 class="page-header">Manual Sign-in</h2>
</div>
</div>
<form class="form" action="" method="post" id="visitor_form" enctype="multipart/form-data">
<?php include_once('../forms/prebook_form.php'); ?>
</form>
</div>
And this is the form:
<fieldset>
<div class="form-group">
<label for="f_name">First Name *</label>
<input type="text" name="first_name" value="<?php echo $edit ? $tb_bookings['first_name'] : ''; ?>" placeholder="First Name" class="form-control" required="required" id = "first_name" >
</div>
<div class="form-group">
<label for="l_name">Last name *</label>
<input type="text" name="last_name" value="<?php echo $edit ? $tb_bookings['last_name'] : ''; ?>" placeholder="Last Name" class="form-control" required="required" id="last_name">
</div>
<div class="form-group">
<label for="email">Email</label>
<input type="email" name="email" value="<?php echo $edit ? $tb_bookings['email'] : ''; ?>" placeholder="E-Mail Address" class="form-control" id="email">
</div>
<div class="form-group">
<label>Visiting Date</label>
<input name="visiting_date" value="<?php echo $edit ? $tb_bookings['visiting_date'] : ''; ?>" placeholder="Visiting Date" class="form-control" type="date">
</div>
<div class="form-group">
<label>Visiting</label>
<input name="visiting" value="<?php echo $edit ? $tb_bookings['visiting_date'] : ''; ?>" placeholder="Who are they visiting?" class="form-control" id="visiting">
</div>
<div class="form-group text-center">
<label></label>
<button type="submit" class="btn btn-warning" >Save <span class="glyphicon glyphicon-send"></span></button>
</div>
</fieldset>

Answer 1

maybe something like this...
if (isset($_POST['submit'])) {
$to = $_POST['email'];
$name = $_POST['first_name'];
$subject = 'Welcome ' . $name;
$message = 'You have been booked in';
$headers = 'From: noreply#blah.com' . "\r\n" .
'Reply-To: noreply#blah.com' . "\r\n" .
'X-Mailer: PHP/' . phpversion();
mail($to, $subject, $message, $headers);
}