Software that provides a method of managing your website is commonly called a CMS or “Content Management System”. Many blogging software programs are considered a specific type of CMS. They provide the features required to create and maintain a blog, and can make publishing on the internet as simple as writing an article, giving it a title, and organizing it under (one or more) categories.
While some CMS programs offer vast and sophisticated features, a basic blogging tool provides an interface where you can work in an easy and, to some degree, intuitive manner while it handles the logistics involved in making your composition presentable and publicly available. In other words, you get to focus on what you want to write, and the blogging tool takes care of the rest of the site management.
WordPress is one such advanced blogging tool and it provides a rich set of features. Through its Administration Panels, you can set options for the behavior and presentation of your weblog. Via these Administration Panels, you can easily compose a blog post, push a button, and be published on the internet, instantly! WordPress goes to great pains to see that your blog posts look good, the text looks beautiful, and the html code it generates conforms to web standards.
If you’re just starting out, read Getting Started with WordPress, which contains information on how to get WordPress set up quickly and effectively, as well as information on performing basic tasks within WordPress, like creating new posts or editing existing ones.