Employment based green cards are made available to individuals whose labor or work skills are needed to fill gaps in the United States workforce. The first and most important step in taking this route in seeking a green card is to have a job offer from a United States employer (there are exceptions for those with “exceptional abilities” or those who are able to obtain a National Interest Waiver). The second step is that the employer must be willing to sponsor you for a green card.
Green cards through employment are divided into five preference categories, each of which has separate requirements that need to be met by the foreign national. In each category, only a limited number of green cards are given out each year. Please see the below links for more information regarding employment based green cards.