It will largely depend on the type of business, type of industry, number of employees, etc., but your responsibilities may generally involve supervising other administrative employees, being responsible for any maintenance or repair work that needs to go on in the office, and some Human Resources responsibilities. Job advertisements will usually detail the expectations for the job.
Susanne recommends the following next steps:
- Read "Office Administration" on Wikipedia: https://en.wikipedia.org/wiki/Office_administration
- Learn more about the profession at the International Association of Administrative Professionals: https://www.iaap-hq.org