Staff Members are needed to finish certain Community Buildings and Landmarks. Staff Members can either be bought for City Cash, filled with Bonus Crew or you can hire your Neighbors. A neighbor can only fill one position in a Community Building but can be hired in several different ones. Once the building is opened the building will run itself and your Neighbors are not required to do anything from the point that they accept the position.
The chart below shows all the community buildings requiring staff members.