A non-US citizen who wants to visit United States of America must apply and obtain a US Visa specific to their purpose of visit. The Visa is stamped/placed in the traveler's passport. Certain international travelers may be eligible to travel to the U.S. without a visa if they meet the requirements for visa-free travel.
Based on the purpose of the trip you have to apply for a specific visa. Basically, there are two types of US visas: Immigrant visa and Nonimmigrant visa. If the visit entails short period of stay for business, education, pleasure, medical treatment, or tourism, then you have to apply for a Non Immigrant or B-1/B-2 visa. If your intention is to stay permanently in US and be a legal resident there, then you should apply for an Immigrant visa.Getting a visa is not a guarantee for entry to US. Permission to enter the country is dependent on the Department of Homeland Security (DHS) and Customs and Border Protection (CBP) officials.
The purpose of your travel and other facts related to your travel plans will determine what type of visa is required under American Immigration law. It's important to have information about the type of nonimmigrant visa you will need for travel, and the steps required to apply for the visa at a U.S. Embassy or Consulate abroad.
Tourist visa to USA is a short-term Nonimmigrant US visa for persons intending to enter the United States temporarily for pleasure or tourism. B-1/B-2 visas come under the category of Non Immigrant Visa (NIV). Often the 2 are issued as one visa - B-1/B2 visa. You do not have to apply for a visa to US if you are covered under US Visa Waiver Program
For how-to-apply for tourist visa information, documentation requirements and more, see the complete details on USA Tourist visa
If you are planning business-related travel to the United States on a temporary basis, you should request for a business visa (B1 Visa). B-1 visa can be applied by individuals when their purpose of visit to US is Business: meet a business associate, close a business deal, attend scientific, educational, and other business conventions/ seminars, attend trade shows, attend a company meeting etc. More details on criteria to obtain B-1 visa: Business Visa to USA (B1 Visa)
If you are planning to visit United States for a medical reason a B-2 visa will be issued. Medical reasons may include seeking medical treatment and advice in USA.
Read more about requirements and guidelines for US visa for medical treatment purpose.
Immigrants living and working in United states may invite parents, relatives, and friends from their home country to visit them in USA. Parents who wish to visit their children in USA, can qualify for visitor visa (B1/B2) visa. This trip can be sponsored by their children. Since there are strict requirements and criteria to get a US visa including a strong financial proof, a sponsored trip can make your case easy.
See a complete step-by-step process to get US Visitor Visa for parents.
*Immigrant vs. Non-Immigrant Visa
There are two types of USA Visas, immigrant and non-immigrant. In an immigrant visa, the applicant is applying for permanent residence in the United States. With a nonimmigrant visa, the applicant is visiting the United States for a temporary period of time for tourism, medical treatments, business, temporary study or temporary work. A visitor visa is a non-immigrant visa.