WordPress is a website development tool with which you can define what is displayed in your website as well as how it is displayed. It is also a Content Management System that keeps track of all of your website content (text, pictures, videos, etc.), providing version control, indexing, and other content management functions.
WordPress is the most widely used website creation tool in the world with more than 18 million active websites. The next most common website creation tools are Adobe Dreamweaver & Joomla! each with about 2.5 million active websites. The large number of active WordPress sites gives some assurance of the robustness of the core software. It also means that there are plenty of WordPress web designers and developers able to help you with your site.
The core software and many of the themes and plugins for WordPress are Open-Source. This means that rather than it being sold by an organisation for profit, it is developed by a community of individuals and organisations and freely distributed. WordPress continues to be actively developed with improvements and extra functionality being released regularly. You can download WordPress free from the WordPress webite.
There are thousands of themes and plugins that can be used with WordPress, many of which are open-source and free. Broadly speaking, themes govern the layout of the website and plugins provide additional functionality. This allows you to do almost anything in terms of the look and feel of the website and its functionality. Furthermore, anyone with the necessary HTML, CSS, and PHP skills can make specific changes through editing their website theme.
The online WordPress community is a fantastic resource. There are countless people working with WordPress at all levels who are more than happy to help. Often the problem you are struggling with has been faced by other people and the answer is already on the Internet. You soon get good at writing Internet search queries that give you the answers you need!