With simple HTML you can't send emails, you need PHP or any other Server-Side programming language
Example of HTML email sending with PHP:
<?php
$to = "PUT_RECIPIENT_EMAIL_ADDRESS_HERE";
$subject = "PUT_SUBJECT_HERE";
$mail_body = '<html>
<body bgcolor="#573A28" topmargin="25">
Put HTML content here with variables from PHP if you like
Variable display Example: ' . $subject . '
</body>
</html>';
$headers = "From:youremail@yoursite.comrn";
$headers .= "Content-type: text/htmlrn";
mail($to, $subject, $mail_body, $headers);
?>
to use email subscription you need a table in your database wich stores emails who subscribed to your newsletter, if a user hits "unsubscribe" you have to execute a MySQL query to remove it from your database:
table: subscribed_users(email)
SQL code to add new users to the newsletter:
INSERT INTO subscribed_users VALUES 'put_email_to_subscribe_here'
SQL code to remove users from the newsletter:
DELETE FROM subscribed_users WHERE email = 'put_email_to_unsubscribe_here'
Of course if you don't know how to use php or mysql, you need to study this two languages in order to do your newsletter subscribing.
If you don't want to learn php and mysql you can watch this page, there are some scripts that may help you, but i think you have to learn at least php in order to use them: