The narthex is an entrance hall or porch located at the western end of some churches. It serves as a transitional space between outside and inside.
Narthex cheat sheet for homework
Aisle: An aisle is a passageway on either side of the nave, separated by rows of columns or piers.
Portal: A portal refers to an elaborate doorway or entranceway leading into a building.
Vestibule: A vestibule is another term for narthex, used interchangeably in some contexts.