Send email with PHP from html form on submit with the same script

Question

When a user has finished filling out an HTML form and has decided to email the data from the form, I want to send an email using PHP. I want to carry it out using the same script that shows the form-containing web page.

I found this code, but the mail does not send.

<?php 

if (isset($_POST['submit'])) {
    $to = $_POST['email']; 
    $subject = $_POST['name'];
    $message = getRequestURI();
    $from = "zenphoto@example.com";
    $headers = "From:" . $from;

    if (mail($to, $subject, $message, $headers)) {
        echo "Mail Sent.";
    }
    else {
        echo "failed";
    }
}

?>

What is the code to send an email in PHP?