There are several answers from the authorities that you can see during a status check of your ESTA application. Your application may be approved or rejected, or the decision may still be pending. Depending on the answer, you should proceed differently.
Authorization Approved: If you can see this answer, you have been granted the ESTA entry permit and you can enter the USA. You can print out your ESTA or just start your trip without a printed out confirmation. Please keep in mind to take your passport with you.
Travel not Authorized: In this case, the ESTA request was rejected. If you still want to enter the U.S., you now need a normal B visa (B-1 visitor visa for business purposes or B-2 entry visa for private purposes). You can also submit a brand new application however, the result will be the same.
Authorization Pending: This means that your application has not yet been decided. Simply log in 1-2 days later to the website again to see if anything has changed. If your application is pending for several days, you should contact the authorities helpdesk to find out if there are technical issue with your application.