Final answer:
The final 's' a) indicates possession or association with an apostrophe and -s for singular nouns, and with an apostrophe alone for plural nouns ending in -s. It is also used to b) pluralize nouns.
Step-by-step explanation:
The functions of the final "s" ("'s" and "s'") on common English nouns include a) indicating possession or association and b) pluralizing nouns.
For example, to show possession with a singular noun, we add an apostrophe and -s (e.g., the owner's insurance). Singular nouns that end in -s and are pronounced are treated similarly (e.g., the waitress's coat).
In the case of plural forms that do not end in -s, we also add 's, as in the children's game. However, for plural nouns that end in -s, we simply add an apostrophe after the final -s, as in the three friends' cars.
The final 's' is never used to introduce subordinate clauses or to emphasize the main subject.