Siding your home to protect it against the elements involves more than just the walls themselves. The eaves where the roof extends out past the walls need to be covered, as well.
The soffit section is below the eaves, running from the edge of the roof to the wall of the house. The fascia is the visible section along the edge of the roof, hiding the soffit.
You can choose among a variety of styles and types, or you can create your own soffit and fascia combination.
http://homeguides.sfgate.com/choose-soffit-fascia-48016.html