How to display Categories as a index page style (wordpress)

<div id="main" role="main">
    <header id="introduction" class="contain">
        <hgroup>
        <?php
            $title = __( 'Archives', 'parament' );
            $description = '';
            if ( is_tag() ) {
                $title = single_tag_title( '', false );
                $description = tag_description();
                if ( empty( $description ) )
                    $description = sprintf( __( 'All posts tagged %1$s', 'parament' ), $title );
            } elseif ( is_category() ) {
                $title = single_cat_title( '', false );
                $description = category_description();
            } elseif ( is_day() ) {
                $description = sprintf( __( 'All posts for the day %1$s', 'parament' ), esc_html( get_the_date( __( 'F jS, Y', 'parament' ) ) ) );
            } elseif ( is_month() ) {
                $description = sprintf( __( 'All posts for the month %1$s', 'parament' ), esc_html( get_the_date( __( 'F, Y', 'parament' ) ) ) );
            } elseif ( is_year() ) {
                $description = sprintf( __( 'All posts for the year %1$s', 'parament' ), esc_html( get_the_date( __( 'Y', 'parament' ) ) ) );
            } elseif ( is_author() ) {
                the_post();
                $description = sprintf( __( 'All posts by %1$s', 'parament' ), esc_html( get_the_author() ) );
                rewind_posts();
            }

            if ( ! empty( $title ) ) {
                echo '<h1 id="page-title">' . $title . '</h1>';
            }

            if ( ! empty( $description ) ) {
                echo '<h2 id="page-tagline">' . $description . '</h2>';
            }
        ?>
        </hgroup>
    </header>

    <?php if ( have_posts() ) : ?>
        <?php while ( have_posts() ) : the_post(); ?>
            <?php get_template_part( 'content', get_post_format() ); ?>
        <?php endwhile; ?>
    <?php else : ?>
        <?php get_template_part( 'content', '404' ); ?>
    <?php endif; ?>

    <nav id="posts-nav" class="paged-navigation contain">
        <h1 class="assistive-text"><?php _e( 'Posts navigation', 'parament' ); ?></h1>
        <div class="nav-older"><?php next_posts_link( __( '&larr; Older Entries', 'parament' ) ); ?></div>
        <div class="nav-newer"><?php previous_posts_link( __( 'Newer Entries &rarr;', 'parament' ) ); ?></div>
    </nav>

</div><!-- end main -->

<?php get_sidebar(); ?>