This site you are looking at is a WordPress blog; this is another. WordPress has a huge variety of themes to choose from, currently there are 146 free themes and themes are added regularly. You’ll see the theme name at the bottom of the screen – this blog uses the Greyzed theme). Anyone can create their own blog. Once you have a WordPress account (WordPress have a step by step guide here) it is very easy to create posts and there is plenty of help available – see for example Learn WordPress.
Another popular blogging platform is Blogger.