I am assuming that you are referring to the article "Shitty First Drafts" by Annie Lamott and "Writing Drafts" by Richard Marius.  Because you did not include the authors, this is just my assumption.  But clearly you are reading two different professional authors' articles about their own writing processes.  To compare and contrast the articles, you don't really need to know what brainstorming "should" look like on paper.  In fact, the point of reading these two different articles is to indicate to you that different writers follow their own distinct processes for drafting.

One of the best ways to begin your comparison-contrast is to create a Venn diagram.  As you read the two articles, use different colored  pens or markers to annotate or highlight similarities and differences.  For example, you could use a green pen for ideas distinct to Lamott, a red pen for ideas that are solely Marius's, and a blue or black pen for ideas that they have in common.  Then in your Venn diagram, with two intersecting circles or ovals, write the approaches the two writers have in common in the part that overlaps, with their distinct or unique ideas in the parts of the circles that don't intersect. 

You can also use a T-chart for similarities and another T-chart for differences.  Then, whether you find the Venn diagram or the T-charts more useful, write your essay by pointing out in one paragraph the ideas distinct to Lamott, in another the ideas that are solely Marius's and then in a third paragraph the ideas about which both professional writers agree.  Good luck!