I want to display the all the posts that are inside a certain subcategory

You can use the get_posts() function and create a custom template file for that! This way you can take advantage of all the arguments that function makes use of.
For example, to show all posts from a category that has id=47 you would do the following:

<ul>
<?php
global $post;
$args = array( 'numberposts' => 999, 'category' => 47, 'orderby' => 'post_date', 'order' => 'DESC',);
$myposts = get_posts( $args );
foreach( $myposts as $post ) :  setup_postdata($post); ?>
    <li><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></li>
<?php endforeach; ?>
</ul>

This will echo the titles of 999 posts (each title linking to the post itself) and it will format them as a list with the <ul>, <li> that we used.
Of course you’ll have to customize that to suit your use-case but this is a working principal.

I hope that helps!

Cheers,
Ari.