4 – Paste the following BEFORE (immediately after the Title): ID, 'subtitle', $single = true); if($subtitle !== '') { ?>

Note: I’ve attempted to format this a bit. Apologies if it ends up ugly.

1 – Add a custom field entitled ’subtitle’ to a post, as described above.
2 – From the Theme Editor, open the Main Index Template (index.php)
3 – Search for the opening paragraph declaration entitled class=”post-info”
4 – Paste the following BEFORE (immediately after the Title): ID, ’subtitle’, $single = true); if($subtitle !== ”) { ?>
5 – Save and open the Single Post Template (single.php)
6 – Repeat Steps 3/4
7 – Save and open Stylesheet (style.css)
8 – Search for post-info
9 – Wherever you have your post-info defined (look for font-size, color, margin, etc), add , #content. subtitle before the opening bracket ({)
10 – Immediately below (after the closing bracket), paste in the following: #content .subtitle { color: #265e15; font-style: italic; padding-bottom: 10px; }
11 – Of course, change the color/font to match your theme…
12 – Now, test! Open up your main page (index.php), and ensure all is displayed correctly. Also, open up a single post and make sure it is also displayed correctly.