Doors used to be “hung” in a jamb built by a carpenter on site. Today however, most doors come from the millworks already hung in a jamb (aka “prehung”). The manufacturer will assemble the door jambs, slab(s), and threshold into one unit that can be easily installed. Often, brickmould (an exterior trim) is also installed to the exterior of the jamb.
Jambs are available in a variety of wood types, as well as composite materials, making them impervious to rot and termites. Sills come in a variety of finishes, including mill (a silver-colored aluminum), bronze, and gold anodized.