A creditor can file something called a Proof of Claim which is based on an official standard form, and includes such information as: Debtor identity and bankruptcy case number; Creditor identity and mailing address; Amount of and basis for the claim; and Type of claim.
The deadline for filing proofs of claim is 90 days after the first date scheduled for the Section 341 meeting of creditors. In a Chapter 13 case, most creditors will file a proof of claim in order to be paid in full (if priority) or pro-rata (if unsecured) through your plan. Inaccurate proof of claims can be objected to and resolved before your plan is confirmed.