This window is a once popular way to show the focus of the content on the website. The most used tags are larger than the less ones. You can click on a tag to get to the search results page narrowed down by a chosen tag.
There are many presets to show your article list. But if you don't like any of those - you can always create your own by selecting the "According to template" option in the Image tab of your article list (Article list > Image position > According to template). You do need to know some html and css to do that though.