Apostrophes & Possessives
Apostrophes show possession (the nurse's chart; the nurses' station) or mark contractions (it's = it is); they never form ordinary plurals.
Singular possession adds apostrophe-s; plural nouns ending in s add only the apostrophe (the students’ grades); irregular plurals act singular (the children’s ward). ‘The Smiths’ is a plural, not a possessive — no apostrophe.