Those are located in the footer panel.
The program output is used to show the user information about what is happening in cssed while performing a given action.
Here you can see the output of a validate and dump action on the current document.
The scratch pad and static pad are just text buffers to be used as a dragable clipboard from/to the editor notebook or for notes.
It is divided into a temporary part: the scratch pad, and a permanent one: the static pad. Drag and drop may be performed between both pads.
The terminal (optional) is very handy to perform external operations while editing a document, such as moving files, running a make, or checking the rendering in a browser.
Here it is a mere ls command which has been executed.