[...by the book: html "tell a friend"-php mail]

hi guys... recently I grabbed an php/mysql book. i'm on the php mail chapter. my goald is this:
to do a tell-a-friend page(html- which I made) and the php part.

Now... I managed to receive messages, on my mail, but I'd like to include HTML into that "tell a friend" result...u know...
subject..." SOS wants you to check out this website!" and the content in HTML.
I know I'm kinda' noob, but I'm trying my best...

[code]<?php
$content="html";
mail($to,strtoupper($subject),$content,$from);



?>[/code]

You realise the code is incomplete...I've been hearing something about MIME....which I don't know what's about...pls have a bit patience and inlight me...
Thank you.