People who are not American citizens who come to the United States generally have to obtain a visa. This is a document that identifies your status and your reason for coming here.
Because people have many different reasons for coming to the United States, there are many different categories of visas. However, there are two basic types: immigrant and non-immigrant visas. You need a visa to enter the United States, but the type of visa you need depends on how long you intend to stay
According to U.S. Customs and Border Protection, if you only intend to stay in the United States for a short time, you need a non-immigrant visa. People come to the United States on a non-immigrant visa for many different reasons. Some are vacationing, while others are traveling for business. You may require a non-immigrant visa if you intend to study in the United States or receive medical treatment but then plan to return to your country of origin. A non-immigrant visa deems you eligible to come into the United States but does not automatically grant you entry.
If you intend to live and work permanently in the United States, you need to obtain an immigrant visa. Upon receiving endorsement of your paperwork by a CBP official, your visa grants you lawful permanent resident status. An immigrant visa has an expiration date, so you must present it at a U.S. port of entry before it expires.
If you fall into one of several special categories, you can petition U.S. Citizenship and Immigration Services on your own behalf. More often, you have to have someone sponsor you and make the application, such as an employer or a family member in the United States.