If your group has bylaws, it should include a section on job duties for each office. That should give you a good idea of what is expected. If there are no bylaws/or job descriptions, I would approach the President of your group and ask what/his her expectations are and talk with the previous Secretary.

I have just joined my first PTO. I have been elected secretary of my council. I am looking for any advice on how to be successful of my duties. I look foward to serving my council to the best of my abilitiy.