All travelers to the United States that don't have a US passport are required to have an ESTA or a visa, issued by U.S. Customs and Border Protection. Traveling with an ESTA is only allowed for trips with a tourist or business purpose, and can last a maximum of 90 consecutive days in the US. In all other cases, a visa needs to be applied for.
To apply for an ESTA, the traveler needs to possess a valid passport. Furthermore, a number of general questions will be asked in the application form.
Payment for the ESTA is made right after submitting the form, and can be done through Visa, MasterCard, American Express, or PayPal.
After filling in the form and making the payment, applications are processed right away.