A U.S. visa allows the bearer to apply for entry to the U.S. in a certain classification, such as student (F), visitor (B) or temporary worker (H). A visa does not grant the bearer the right to enter the United States. The Department of State is responsible for visa adjudication at U.S. Embassies and Consulates outside of the U.S.
U.S. Customs and Border Protection (CBP) immigration inspectors determine the admission, length of stay and conditions of stay at a port of entry. The information on a nonimmigrant visa only relates to when an individual may apply for entry into the U.S. DHS immigration inspectors will record the terms of your admission on your Arrival/Departure Record (I-94 white or I-94W green) and in your passport.