Since you acknowledge owing the money, I assume you have no defense other than "I don't have (or don't want to pay) the money I owe them". If that is the total of your defense, here is what you have to look forward to:
1) They will get a judgment against you for the amount that you owe. Further, the court will also assess you the cost of their attorney fees (if any), plus the costs of court, plus interest at the state mandated amount.
2) With the judgment(s) in hand, the creditor can now go about enforcing the judgment. This could include anything from seizing your property, your assets, garnishing wages, etc. depending on where you live and what they allow to be seized.