Responsibilities typically include:

organising meetings and managing databases
booking transport and accommodation
organising company events or conferences
ordering stationery and furniture
dealing with correspondence, complaints and queries
preparing letters, presentations and reports
supervising and monitoring the work of administrative staff
managing office budgets
liaising with staff, suppliers and clients
implementing and maintaining procedures/office administrative systems
delegating tasks to junior employees
organising induction programmes for new employees
ensuring that health and safety policies are up to date