Before going to the U.S., you’ll need to obtain permission. The ESTA form is a travel authorization which will let you travel to the U.S. over a period of 2 years, and which is quicker and easier to obtain than the traditional visa.
The ESTA form is ideal for all travel arrangements to the U.S from participating VWP countries, as it is processed very quickly. For some travellers, they will find that their form has been processed and approved within minutes, and a long processing time still only takes 72 hours. You can find instructions on how to apply here. It is worth noting however that the ESTA form does not completely guarantee your entry to the United States - the U.S Border Authority still have the final say on who can or cannot enter the country, so make sure to keep all of your documentation in order when you arrive.