When you freewrite in your journal, you write down anything that comes to mind. You might decide to set a limit, such as the number of pages or a time limit. Freewriting in your journal is different from reflecting and working through a problem. When you freewrite in a journal, every random idea and impulse goes on the page, and you should write without stopping. You might encounter an idea that you want to explore during the freewrite, and this is an impulse that you should follow. The main thing is to not begin the freewrite with any topic in mind.
Goldberg's rules appear to be based on those developed by Jack Kerouac , whom she cites several times. Kerouac developed 30 "rules" in his Belief & Technique for Modern Prose.  While Kerouac's "rules" are elliptical and even cryptic for beginning writers, they are more comprehensive than Goldberg's for those who have practised prose writing for some time. Kerouac supplemented these with his Essentials of Spontaneous Prose,  and together they form the basis of his prose writing method, a form of narrative stream of consciousness . Kerouac himself cites the "trance writing" of William Butler Yeats as a precursor of his own practice.