There are 2 versions of WordPress. One is run by WordPress.com, the other you run yourself. So, there is in effect only one version of WordPress; its just that the way they are run is different. The distinctions between WordPress.com, WordPress, and WordPress.org can cause some confusion.
WordPress.com is really a blogging hosting platform. This means that you can run a blog on WordPress.com, have many of the standard WordPress features and do it all for free. You have to pay for extra features and your domain will be something like myfirstblog.wordpress.com.
However, it’s not a true/unique website, you don’t have a domain, you don’t have standard domain functions and you are limited in what you can do.
On the other hand you can run a full version of WordPress on your own domain, for example myfirstblog.co.uk. This is also free and you have access to and control of all the functions for your website. However, you have to pay for the hosting of your site. You can set everything up to make your site look and do what you want yourself, but it can get quite complex and may involve coding.
WordPress has become a complex and sophisticated tool although creating the content has been made as easy as possible.
WordPress is an open source product which means that the code behind it is open for people to develop and improve. It is used by millions of people and companies worldwide.