A visa does not guarantee you entry into the United States
. Having a US visa allows you to travel to the US port-of entry and there the permission to enter the US is decided. The Department of Homeland Security, USCIS, U.S. Customs and Border Protection (CBP) officials are the authority who can permit or deny admission to the United States. At the port of entry, if granted entry to the U.S., the Department of Homeland Security, US immigration inspector will provide Form I-94, the arrival-departure record in your passport. Per US immigration laws, you need to leave the United States if your I-94 contains a specific date.