ok so its been a while since i did anything html, i know ive seen this before but im not sure that ive used it, what is it for exactly and is it actually needed?

here is an example of it

<body>
<div id="main">
<!--header-->
<div id="header">
<!--block1-->
<div class="block1">

<!--logo-->
<h1 class="logo"><a href="http://www.posemaniacs.com/">Posemaniacs</a></h1>
<p>Pose Maniacs supports all artists, including art students and people who study illustrations and mangas on your own. This blog is for uploading variety of poses for nude sketching, and introduces other FLASH training tools for drawing. Some donation enables me to make English version. Thanks alot. <a href="http://blog.artandmobile.com/2008/10/random-pose-viewer/">Now posemaniacs is on the iPhone / iPod.</a></p>
</div>
ah I see, thank you both very much for your answers.