how to use mail function in php | mail in php | mail code in php | mail script in php

how to use mail function in php | mail in php | mail code in php | mail script in php 

<?php
$to  = 'saddam1234321@gmail.com';
$subject = 'test mail';
$message = 'this is dummy mail';
//mail(to, subject, message, header, variable)
mail($to, $subject, $message);
?>  

1 To is reciver email adress
2 subject is short text
3 message is brief dicustion