If you are in the United State and your visa number is current, meaning that no visa backlog for EB2 category for your country of birth, you may file adjustment of status (AOS) application along with your NIW petition. However, USCIS will not adjudicate you AOS application until your NIW is approved. You may also file AOS application immediate upon approval of your NIW petition. In this case, you usually could receive your green card within one year of filing your AOS.
If you are in your home country and your visa number is current at the time your NIW being approved, your case will be transfer to National Visa Center (NVC) for further processing. You will receive notice from NVC within 2 months of approval, instructing you to submit civil documents and online application to initiate the Consular Processing process. You will go through visa interview at you home country and come to the US with your immigrant visa. You will then receive your green card after entering the United States.
If your visa number is not current, you would have to wait for your visa number became current to begin the Adjustment of Status application or Consular Processing.