Okay well I solved my own problem. I added a new div, pasted a post loop inside, and to specify the number and type of posts I wanted the column to list, I inserted the following code in the relevant template (for me, that's the index.php file) below the start of the div code "<div class="[name]"> "
$topbox = get_posts('numberposts=3&category=8');
foreach($topbox as $post) :
--content, e.g. post title, thumbnail info, excerpt info goes here--
<?php endforeach; ?>
Edit how you see fit.
Then I changed the width of columns via CSS so they appear on the homepage.
I can't say if my solution is the correct and cleanest way, but so far it's working fine.