Foreign nationals become eligible for green cards based on family or employer sponsorship. They can either get immigrant visas through consular processing or they can go through the adjustment of status process and get green cards if they are in the U.S.
Beneficiaries of immigrant petitions who are living abroad need to go through consular processing to get immigrant visas. But beneficiaries of immigrant petitions who are in the U.S. as non-immigrants can apply for adjustment of status. This process will help them to adjust their status and get green cards while in the U.S. In this case, they need not get immigrant visas from overseas U.S. consulates or embassies.
Consular processing will not take place in the U.S. It will take place at overseas U.S. consulates or embassies in countries where the beneficiaries of immigrant petitions reside. On the other hand adjustment of status will take place in the U.S. This process will allow the applicants to remain in the U.S. and will not require them to go to their home countries to get immigrant visas. They can stay in the U.S. while their applications are being processed.
People in the U.S. applying for adjustment of status, can file applications for work permits and travel documents. They can work and travel legally while waiting for the approval of their Form I-485, Application to Register Permanent Residence or Adjust Status. But this does not apply to the beneficiaries of immigrant petitions who are abroad and who need to go through consular processing.
If an application for an immigrant visa is denied, the decision can be appealed only under limited conditions. But applicants whose adjustment of status applications are denied can file a motion to reopen the case.
People who go through consular processing will be issued immigrant visas and they need to come to the U.S. with those visas and then get green cards. But green cards will be mailed to those who apply for adjustment of status after the approval of their applications.