What does change one proper noun to a possessive pronoun in each sentence mean?

A proper noun is the name of a specific person, place, or thing.

A possessive pronoun is a Word that takes the place of a noun that belongs to someone or something.

Examples:

Jack rode his bicycle to school today. The black bicycle is his. (the possessive pronoun 'his' takes the place of the noun 'bicycle' indicating the the black bicycle belongs to Jack, the name of a specific person)

Note: A possessive adjective is pronoun placed before a noun to describe the noun as belonging to someone or something.

Example: Jack rode his bicycle to school today. The black one is his bicycle.