The Department of State (DOS), also referred to as the State Department, handles all international affairs, and has a wide range of responsibilities within the United States. The Bureau of Consular Affairs is the primary department within DOS that deals with immigration. The Bureau of Consular Affairs encompasses embassies and consulates, adjudicating immigrant and nonimmigrant visa petitions. Nonimmigrant visas permit individuals to travel to the U.S. temporarily for tourism/pleasure, business, temporary employment, education, etc., and are also given for Fiancé visas (K visas). 90 days after K visas are approved, you must get married; then you may apply to adjust your status.
Immigrant visas are for those seeking permanent residency in the U.S., not for temporary visits like the nonimmigrant visa. A U.S. citizen can file an immigrant petition for their spouse, child, or immediate relative. A Lawful Permanent Resident (green-card holder) can file for a spouse or their unmarried child. An employer can file for a potential employee. The immigrant petition must be approved by USCIS before the case is transferred to the Bureau of Consular Affairs where the National Visa Center (NVC) begins visa processing. This step requires an application and the submission of all supporting and financial documents, as well as additional filing fees, to the NVC. This process varies depending on the specifics of the case.