The caller is not really from the IRS. Its a scammer trying to steal money from you.
If you talk to the caller they will tell you that you are about to be arrested for over-due taxes. The only way to avoid arrest is to pay those taxes right this second by giving them your bank account number or credit card number. You also have to "confirm" you social security number and full name. The scammers use that information to spend all of your money and cause other trouble in your name.