A green card allows the holder to live and work in the United States indefinitely. It is evidence of the status of lawful permanent residence and is usually obtained through self-sponsorship, sponsorship by an employer, or family sponsorship.
Selfsponsorship for a Green Card
Individuals of extraordinary ability in the arts or sciences can get a "green card" based upon their accomplishments in their field. Others may qualify for a national interest waiver if they can establish that their work is will greatly benefit the United States. In either case, no particular employer has to sponsor the person.
Other than the "self sponsoring" situation, employment-based immigration requires that the Department of Labor certify that no qualified U.S. workers are available to fill the position offered to the foreign national and that hiring the foreign national in that position will not negatively impact the wages and working conditions of similarly situated U.S. workers. Labor certifications are used to sponsor professional with degrees, skilled workers such as chefs or even lower skilled workers such as child care providers.
You are eligible to apply for a green card if you are:
the spouse of a United States citizen or permanent resident,
the unmarried child of a United States citizen or permanent resident,
the married child of a United States citizen,
the parent of a United States citizen who is 21 years of age or
older, are the brother or sister of a United States citizen.