This one should be easy! The interviewer wants to get a better understanding of your background. Break down your tasks by each past employer. State the name of the company, your job title, and the typical tasks you completed in each role. This will allow the interviewer to understand what tasks you're already skilled with and will help the interviewer implement a stronger training plan customized for you if you're selected for the position.
Bear in mind any non-disclosure agreements you've signed. It's not uncommon to sign an NDA in the accounting field. You're dealing with sensitive information, and if you leak that information, it could cost the company investors, which is why most companies require you to sign something. If you've signed an NDA, be vague about the company while going into detail about the work you completed.