WordPress is an open source CMS(content management system). A content management system is basically a way of organizing all your information in a database for your website to display. It is the magic behind WordPress being so user friendly and customizable.
So what is the difference between WordPress and a regular website? Nothing, you can build the same things in both except WordPress helps give you structure and tools to do it faster. Think of your website like a house. WordPress is like going to the store and buying everything precut and ready to nail together. The boards all fit right and work together. No boards are too long or cut funny. So your house is built more securely. WordPress gives you tools to build your house faster and better.
WordPress makes up more than 27% of all websites. That is the highest percentage of any content management system. WordPress is opensource so it is a community project. It has a giant friendly community with a lot of support and documentation.
How do you install it? Most hosing companies have a 1 click install or will install WordPress for you. If you want to learn how to do it yourself, WordPress has what is called the Famous WordPress 5 Minute Install. It is a very simple, step by step process. Here is a great blog post that tests out that 5 minute process. https://www.elegantthemes.com/blog/tips-tricks/putting-the-famous-wordpress-5-minute-install-to-the-test