To use category modules on Joomla, you can follow these steps:
1. Log in to your Joomla backend.
2. Go to Extensions > Modules.
3. Click on the “New” button to create a new module.
4. Select the “Articles Category” module type from the list.
5. Configure the module options according to your needs, such as selecting the category you want to display, the order, and the number of articles to show.
6. Save the module settings and assign it to a position on your website where you want it to appear.
7. Preview your website and check that the category module is displaying correctly.
You can also customize the style of the category module by editing the CSS code or using a template override. The exact steps may vary depending on your Joomla version and template, so you may need to consult the documentation or seek help from a Joomla developer.