I am U.S. citizen. My son is in U.S. and he has married. How could he adjusts his status in U.S. if the Form I-130 is approved for him? In another words, what is the availability of a visa number for him? and what is the process for adjusting status for him?

Answer:

To adjust status in the United States or to get U.S. Green Card, an immigrant visa number must be readily available to the alien immigrant. Each year, a certain number of immigrant visas are available for alien immigrants. The available immigrant visa numbers and their current "priority dates" can be checked at the monthly Visa Bulletin issued by the U.S. Department of State.

The Priority Date is the date on which an immigrant visa petition is filed with the USCIS. Therefore, an alien immigrant can apply to adjust status only when his or her priority date is "current". The immediate relatives of U.S. Citizens are exempted from this requirement as they are not subject to the immigrant visa quota system. But other relatives of U.S. Citizens, such as U.S. citizen's married child or U.S. citizen's brother or sister, are subject to the immigrant visa quota system.

By filing USCIS form I-485 - Application to Register Permanent Residence of Adjust Status, an alien immigrant can adjust his or her status to a lawful permanent resident within the United States, if the alien immigrant can meets the requirements and is not subject to any ground of inadmissibility. Also, the alien immigrant needs to submit other mandatory governmental forms, relevant documents, and application fees to USCIS.

http://www.greencardfamily.com/question/question2014/I485_Adjusting_Status_0422.htm