This is a very simple version of a Categories sub-menu implemented in the sidebar.php. Once a category is clicked, the sidebar should show the following:
The default template shows the sidebar only on selected pages. I often make a design decision to display the sidebar on every or nearly every page. This is a fairly straightforward set of template edits. As an example, we will work with the template single.php. This is the template which displays individual posts
To gain further understanding of which template files are used when view a WordPress site visit WordPress Site Architecture.
There a many reasons why you might not want all categories to display in the side bar. Some possible reasons are:
Use the Text Widget to add HTML to the sidebar. This makes it very easy to add a wide variety of features to your site. I will demonstrate a few simple examples.
