This window is used to place html-formatted text into any zone. You don't need to know HTML to put the text in. However, placing images or complex elements will need such knowledge. You can also use this window to place HTML-code of counter, soclal-media widgets etc. on your page.
Example of HTML-formatted text is shown below.
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.