How to change page menu items to category ones.

I know there is a WordPress article on how to link to a category listing of posts, but when trying to enter those specific lines of code it doesn’t work. Menu code is below. Can anyone help me identify what to remove and replace with so I can link to specific category posts rather then the pages?

<div id="menu_nav">
      <ul>
        <?php if(is_home()) { echo '<li class="current_page_item">'; } else { echo '<li class="page_item">'; } ?><a href="<?php bloginfo('url'); ?>" title=”Home”>Home</a>
</li>    <?php wp_list_pages('title_li='); ?>    </ul>
    </div>