The documentation that will be necessary for traveling to the US will depend upon how long you plan to stay. Visitors of up to 90 days can stay without getting a visa, by applying through the Visa Waiver Program (VWP). Only people from certain countries are granted this ability and there are currently 37 participants in the program. Different rules govern travel from Canada, Mexico, Bermuda and other nearby islands.
Before traveling without a visa, it is necessary to be approved by the Electronic System for Travel Authorization (ESTA), which is run by Customs & Border Protection (CBP). The processing and authorization fees cost only $14. If you are staying for more than 3 months, a more comprehensive travel visa will be necessary. Should this be the case, your eligibility and requirements will be determined by the nature of your visit.
If you have any questions about what type of United States travel visa you will need, please contact an Immigration Lawyer for more information. He will be able to clarify any of your concerns and help you better understand the process involved.