* The apostrophe comes *after* the possessor, not before. For example, "The dog's bone" in English becomes "L'os du chien" in French.
* The apostrophe is used with masculine singular nouns ending in "-s" or "-x". This is to avoid having two consecutive "s" sounds. For example, "The cat's tail" becomes "La queue du chat".
* The apostrophe is used with plural nouns, regardless of their ending. This is because the plural form already indicates possession. For example, "The students' books" becomes "Les livres des étudiants".
Let me know if you have any other questions!