WordPress.com is something like Google's Blogger.com - with it you get yourdomain.wordpress.com and you can free your blog for WordPress. You just need to make an account and select a topic - and you're ready, in a few clicks.
WordPress.com can work with your domain, but it limits in terms of customizing the site itself. For example, you can only choose a topic from the offered, you can not change it yourself at no extra cost.
You can use WordPress.org only if you have your own domain and hosting. It is downloaded as .zip or .tar.gz compressed archive, unpacked and uploaded via FTP to the root of the site (more details about installing in the next sequel of Feeton). It is necessary to separate only a few minutes to enter the essential data, and the site can start working. With this variant you will have much greater control over your data. You will be able to install multiple themes and plug-ins. One sentence - there are no restrictions.
The continuation of the text as well as the complete series of articles will focus on wordpress.org.