I don't understand what Usha intended with her post—most likely a free advert for her firm—but if you need more information on the payroll function, you can either do a course (Google for such courses, of course) or reach out to someone with a payroll provider (Usha's firm, for example) so you can get a practical, bottom-up approach. Studying and gaining certification only leads to conceptual knowledge and not functional expertise.
Hope this helps.