You must go through a multi-step process to become an immigrant based on employment:

• In most employment categories, a U.S. employer must complete a labor certification request for you with the Department of Labor
• The USCIS must approve the immigrant petition that was filed on your behalf, usually by an employer
• If an immigrant visa number becomes available to you, you may apply to adjust to permanent resident status if you are in the U.S. If you are outside the U.S. when an immigrant visa number becomes available, you will be notified to go to the U.S. consulate or embassy with jurisdiction over your area to complete the processing for an immigrant visa

In certain circumstances, some steps are not needed, or certain steps can be completed simultaneously.