Unable to send mail using PHP

Question

Am using this following code to send mail using php

<?php
if (isset($_POST['email'])) {
    // EDIT THE 2 LINES BELOW AS REQUIRED
    $email_to = " lawrence@gmail.com";
    $email_subject = "Your email subject line";

    function died($error) {
        // your error code can go here
        echo "We are very sorry, but there were error(s) found with the form you submitted. ";
        echo "These errors appear below.<br /><br />";
        echo $error . "<br /><br />";
        echo "Please go back and fix these errors.<br /><br />";
        die();
    }

    // validation expected data exists
    if (!isset($_POST['first_name']) ||
            !isset($_POST['last_name']) ||
            !isset($_POST['email']) ||
            !isset($_POST['telephone']) ||
            !isset($_POST['comments'])) {
        died('We are sorry, but there appears to be a problem with the form you submitted.');
    }
    $first_name = $_POST['first_name']; // required
    $last_name = $_POST['last_name']; // required
    $email_from = $_POST['email']; // required
    $telephone = $_POST['telephone']; // not required
    $comments = $_POST['comments']; // required
    $error_message = "";
    $email_exp = '/^[A-Za-z0-9._%-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}$/';
    if (!preg_match($email_exp, $email_from)) {
        $error_message .= 'The Email Address you entered does not appear to be valid.<br />';
    }
    $string_exp = "/^[A-Za-z .'-]+$/";
    if (!preg_match($string_exp, $first_name)) {
        $error_message .= 'The First Name you entered does not appear to be valid.<br />';
    }
    if (!preg_match($string_exp, $last_name)) {
        $error_message .= 'The Last Name you entered does not appear to be valid.<br />';
    }
    if (strlen($comments) < 2) {
        $error_message .= 'The Comments you entered do not appear to be valid.<br />';
    }
    if (strlen($error_message) > 0) {
        died($error_message);
    }
    $email_message = "Form details below.\n\n";

    function clean_string($string) {
        $bad = array("content-type", "bcc:", "to:", "cc:", "href");
        return str_replace($bad, "", $string);
    }

    $email_message .= "First Name: " . clean_string($first_name) . "\n";
    $email_message .= "Last Name: " . clean_string($last_name) . "\n";
    $email_message .= "Email: " . clean_string($email_from) . "\n";
    $email_message .= "Telephone: " . clean_string($telephone) . "\n";
    $email_message .= "Comments: " . clean_string($comments) . "\n";
// create email headers
    $headers = 'From: ' . $email_from . "\r\n" .
            'Reply-To: ' . $email_from . "\r\n" .
            'X-Mailer: PHP/' . phpversion();

    @mail($email_to, $email_subject, $email_message, $headers);
    ?>
    <!-- include your own success html here -->
    Thank you for contacting us. We will be in touch with you very soon.
    <?php
}
?>

This is contact form in my website user will send their review from my website to admin e-mail but here am unable to send mail with above code can someone help me am using this in local-host can some one help me