I'm not american so i need about something i don't get. when is it -was served- and when is it -is/was being served ? (passive tense)

Read the excerpt below and answer the question. she was a small woman, short and straight-waisted like a child in her brown cotton gown. her forehead was mild and benevolent between the smooth curves of gray hair; there were meek downward lines about her nose and mouth; but her eyes, fixed upon the old man, looked as if the meekness had been the result of her own will, never of the will of another. in at least one hundred words, explain how this excerpt uses explicit and implicit details to describe sarah penn.