A green card is the official certificate issued to a foreign national by the US Immigration Service granting the card holders permanent residency in the USA. A green card permits you to live and find employment in the United States.
The main ways for you to obtain a green card in the United States is to submit employment based green card application, or a family member green card application.

You can apply for employment based green card if you belong to the priority workers category, professionals with advanced degrees, skilled professional workers, current or former employees of the US government or if you belong to immigrant investors category.

You can apply for family based green card if you have relatives with US citizenship or if you have relatives in the US with permanent resident status.

Other ways to obtain a green card include DV lottery, business investment green card, fiancée green card, adoption green card, and asylum and refugees green card.