Main?If you want people to be able to see actual HTML code on your webpage, simply use the <xmp> tag (and its closeing tag).
This code could come in handy if you ever want to teach people HTML yourself.
Example:
<xmp>
<html>
<head>
<title>BLAH</title>
</head>
<body>Blah</body>
</html>
</xmp>
However, this tag is somewhat obsolete, so if you are paticularly uptight about "clean code" then using a combination of the <pre> tag and the character codes < for <, and > for > would be better.