A more thorough explanation:

A green card, also known as a Permanent Resident Card, is a plastic photo identification card that proves a person's legal permanent residency in the United States. It allows the holder to live and work permanently in the United States. The card serves as a U.S. entry document, enabling holders to return to the United States after temporary absences, and it proves their right to work in the United States. The green card expires after a certain number of years and must be renewed, but the holder's permanent residence itself does not expire, only the ability to prove it using the card.

John is a citizen of Canada who has been living and working in the United States for several years. He applied for and received a green card, which allows him to continue living and working in the United States permanently. He uses his green card as proof of his legal status when he travels outside of the United States and when he applies for jobs.

Another example is Maria, who is originally from Mexico. She received her green card after marrying a U.S. citizen. With her green card, she is able to work and live in the United States with her husband and children.

These examples illustrate how a green card allows individuals to live and work in the United States permanently, as well as how it serves as proof of their legal status in the country.