The factory creates paragraphs and paragraph-like objects (like embedded graphs and pictures).
The factory is gotten by clicking the + in the Edit Journal:
Edit Journal
This is the factory:
A picture of a factory
(Technically, each of the bullet items is a factory, with two unlisted factories – one makes a new paragraph editor when you double click, and one handles drag-and-drop.
(So you could think of this is a factory of factories.)