Catergory/Archives page not working

I’ve been trying to figure out what’s wrong with this archieve.php folder. i have a blog on this site. https://www.msrshirts.com and when i click on media>>blog you see that the blog appears but only one post shows at a time. and then you click on the one page take you to another single post. here is the script i’m using. can anyone help. here is the link to the blog:

https://www.msrshirts.com/?cat=1

<?php get_header(); ?>
	<div id="main">
		<?php if (have_posts()) : ?>
		<?php $post = $posts[0]; ?>
		<?php if (is_category()) { ?>

		<?php } elseif( is_tag() ) { ?>
			<h1 id="category-title">Posts Tagged ‘<?php single_tag_title(); ?>’</h1>
		<?php  } elseif (is_day()) { ?>
			<h1>Archive for <?php the_time('F jS, Y'); ?></h1>
		<?php  } elseif (is_month()) { ?>
			<h1>Archive for <?php the_time('F, Y'); ?></h1>
		<?php  } elseif (is_year()) { ?>
			<h1>Archive for <?php the_time('Y'); ?></h1>
		<?php  } elseif (is_author()) { ?>
			<h1>Author Archive</h1>
		<?php  } elseif (isset($_GET['paged']) && !empty($_GET['paged'])) { ?>
			<h1>Blog Archives</h1>
		<?php } ?>

<h2 class="sharedwearh2"><a>" title="<?php the_title(); ?>"><?php the_title(); ?></a></h2>
<?php the_content(); ?>

		<hr></hr>

<?php if (function_exists("pagination")) { pagination($additional_loop->max_num_pages); } ?>
<?php endif; ?>
</div><!-- End Main -->
<?php include("BlogSidebar.php"); ?>
<?php get_footer(); ?>

[please use the code button instead of blockquote to mark any code]