Here’s an example of a “custom mini-loop.” It’s the code I use to show recent posts in the sidebar (reformatted a bit and after removing the extra attributes on the <a>
tag. If you’re putting this in the footer, you might not need to save off the page’s default query and restore it — but it’ll be needed to show the teaser in the sidebar or recent image in the main part of the page.
The key part here is the use of query_posts. Check there for other parameters and several examples.
<?php
$include_cats = ... whatever makes sense here ....
$temp_query = $wp_query;
query_posts('showposts=5&cat='.$include_cats);
while (have_posts()) {
the_post();
?>
<li>
<?php the_time('m/d'); ?>:
<a href="<?php the_permalink(); ?>" >
<?php the_title(); ?></a>
</li>
<?php
} // end custom loop
$wp_query = $temp_query;
?>
Best wishes as you work through the lessons. I’m afraid I wasn’t that methodical — mostly took it one template tag at a time. It took quite awhile before I had the sense that I could tweak WordPress to do what I wanted (mostly, anyway).
There are, no doubt, plugins to do this, but when I can drop code onto a page, I prefer to do that. On the other hand, something like
https://www.ads-software.com/extend/plugins/show-post-by-selective-category/
may help you out if you’re not (yet) comfortable with the PHP.