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.
Some of the modules in Cornerstone can combine content of "simplier" modules. Articles can contain videos, pictures and even questionnaire forms, that are stored in particular modules. Shop items can store pictures in the Images module, and articles in a linked article module.