I'm going to high school in America, but I don't know if I can apply for a green card.

You can't apply for a green card if you just go to school. Ordinary people can only apply for a green card to work in the United States through hard work. After completing their studies, international students can find jobs, be employed by American companies, or be sent directly to the United States by large companies. After working for several years, they can apply for a green card with the support of the company.

If immediate family members have obtained American citizenship, they can apply for a green card as long as they have lived in the United States for a certain number of years.