Pages in this WordPress theme have one or more sections. Each section is a top layer row in the Page Builder. The page comments area and footer also is a section. The nested rows (row inside row) is not represented as page section, but represented as areas inside page section, that have other design. Please read in the SiteOrigin Documentation about how to work with page builder rows.
You can customize section design via row settings in the page builder. Please read Page Builder about additional row options that are added by the theme and also read Footer and Comments about how to customize this areas.