Each department requires staff members of its own kind. E.g. Pharmacy requires Pharmacists, Wards require Nurses and the operating room requires Surgeons. The only exception is the breakroom, where any staff member can be placed to replenish their stamina. Initially you can assign one staff member to a department, but each department can be upgraded to allow for more slots. A staff member can be assigned to a department by entering build mode and clicking on the + icon. If a slot is occupied by another staff member, that staff member first needs to be removed from the department before another can be assigned.