Joomla
Joomla is a free open-source content management system for publishing web content. When downloading Joomla in your web host account, you have to create or generate strong usernames and passwords to login to the backend of your Joomla site. You have to type in your domain name slash the administrator to successfully log in to your account (www.yourdomain.com/administrator). You can simply create articles, but you need to select a template for your site and in order to do that, you'll need to download the template from JoomShaper. To put articles on your website, you'll need to add a new menu, give it a title, and select the article you want for that menu item. You can also add extensions to gain more search engine optimization, security, page builder, authentication, languages, etc.
WordPress
WordPress is a content management system that is based on PHP and MySQL databases. This works exactly like Joomla except when you login, you need to put in your domain name slash wp-admin (www.yourdomain.com/wp-admin). You can select any variety of themes which Joomla calls templates and add plugins that are the same as Joomla extensions. WordPress calls their documents Pages while Joomla calls there's Articles. If you want available themes and plugins, then I would recommend WordPress because when going into Joomla, there's not much extensions/plugins available and/or updated.