If you are eligible for an ESTA because of your nationality, you can travel with an ESTA to the US for business or pleasure. However, it happens regularly that an ESTA application is rejected. This can have different causes, perhaps you have made a mistake in your application form (for instance you ticked the wrong box), or on the last page you have had to answer ‘yes’ to a question. Whatever the cause, you are not told why you have been rejected.
Has your ESTA been rejected?
In that case you have to apply for a visa. If you travel for pleasure you have to apply for a B2 visa. If you travel for business you have to apply for a B1 visa. A combined B1/B2 visa is also an option.