A collection is a result of a debt owed that has not been paid on time. Once this debt becomes significantly delinquent, such as a medical bill or credit card, the original company that extended you the credit will write your debt off as a loss and sell it to a collection agency. The bill collector who works for the collection agency will contacted you and attempt to recover the money that is owed.
Creditors have different policies but for the most part most credit card companies will send your account to collection once you have surpassed the 180 day make of non payment. The original creditor or collection agency will now report your debt as a collection to all three major credit bureaus and it will show on your credit report as a collection. The lenders report this information without even notifying you but you will see the collection reported on your Trans Union, Experian and Equifax credit report.