Two categories in one archive page

YES. I know there are a lot of results for this question on Google but none of them appear to work for me or the answers are in fuzzy code speech (which means nothing to me).

<?php if ( have_posts() ) : ?>
<?php while ( have_posts() ) : the_post(); ?>
<?php get_template_part( 'content', get_post_format() ); ?>
<?php endwhile; ?>
<?php else : ?><article id="post-0" class="post no-results not-found">
<header class="entry-header">
<h1 class="entry-title"><?php _e( 'Nothing Found', 'shiro' ); ?></h1></header>
div class="entry-content">
<p>
<?php _e( 'It seems we can’t find what you’re looking for. Perhaps searching can help.', 'shiro' ); ?>
</p>
<?php get_search_form(); ?>
</div>
</article>
<?php endif; ?>

Thats all from my archive.php, how do I convert that to show just two categories?

I have already created a new category specific template by simply cutting and pasting the above, adding two categories is beyond me.