People from overseas who wish to enter the USA must get American Visitor Visa which is sanctioned in the passport of the individual. But you also need to know that visa does not guarantee entry into the United States. Instead, it just defines the eligibility of the individual who wants to enter the United States.
The decision of providing you a Visa is totally dependable on the Department of Homeland Security (DHS), Customs and Border Protection (CBP).
There are two types of US visitor visa and further, they are classified into Immigrant Visa and Non-immigrant visa. Immigrant visas are for those people who wish to travel here and live permanently in the US. Non-immigrant visas are for the people who travel the USA only for leisure purposes.
There are a specific set of conditions that are required by the person to qualify for the American Visitor Visa. The person must provide the proof that the purpose of the trip to the US is for only business, pleasure or for medical treatment and the individual is not planning to remain in the USA for a longer period than the visa.
Also, the person must present evidence of funds to cover costs in the United States, proof of compelling social and economic ties abroad, and that he/she has a residence outside the USA and also have other necessary ties that will guarantee the individual leaves the US at the end of the visit period.
A person or a group of people can generally apply for American Visitor Visa at the U.S. Embassy of their country. It is suggested that you should apply months prior to your travel plans as there are many legal procedures you have to take.
Once your American Visitor Visa has confirmed, the CBP will decide if you will be allowed to enter the USA or not. The customs and border protections also decides the length of the stay in Form I 94.