Article as such is just a container (a structure) for article elements. The real content resides in article elements: headline, body, images, multimedia etc.
An article without any element is useless. Therefore, when you create a new article, GN4 typically automatically creates also the body element.
You can add more elements to the article at any time, while you have permissions to access the folder where the article resides.
For further information, see
Add or remove article elements
Formats and article element types
Global variable for auto-added article elements
About auto-creation of article elements