How to include categories on top of my posts?

How do i include categories in my main index page. My index page.php is as follows. Anyone?

<?php
get_header();
if (have_posts()) {
    while (have_posts()) {
      art_post();
    }
    art_page_navi();
 } else {
    art_not_found_msg();
 }
get_footer();