You organise and coordinate the transmission of the department's information for your manager. You type and present notes and documents, generally confidential.
You handle, use, follow-up some of the department's information (everyday correspondence, specific topics). You open the incoming post and organise agendas.
You answer and filter telephone calls, establish direct contact with your manager and the outside world. You may also manage and train a team of employees or be in charge of following-up the department's budget.