Generally, a citizen of a foreign country who wishes to enter the United States must first obtain a visa. Visitor visas are nonimmigrant visas for persons who want to enter the United States temporarily for business (visa category B-1 includes attending a scientific, educational, professional or business conference), tourism, pleasure or visiting (visa category B-2, includes tourism and vacation), or a combination of both purposes (B-1/B-2). Please see the U.S. Visa's website for more information.
(*Note: At the Visa website link above, you can set/edit the location in which you are located in order to make it easier for you to navigate the webpage. This is located in the top right corner of the website under “Set Location” and “Set Nationality”. )