All travellers passing through the US are required to fill in an online form to obtain authorisation for a US Visa Waiver. The form can be found here: https://esta.cbp.dhs.gov
This will take you the US Department of Homeland Security web page where you can apply. Once there, please click on the New Application button and follow the instructions.
Although this can be filled in up to 72 hours before travel, we recommend that you fill in this form as soon as possible so any issues can be identified immediately. Please make sure that this form is filled out for all the passengers on your booking.
Please note that although you can fill in all the details requested on the online form only the fields marked with a "*" are required. If you have any questions about this please don’t hesitate to contact us.