When a debtor files bankruptcy, it stops his creditors dead in their tracks. A bankruptcy trustee is appointed to adminster the case, and if there is any money to be paid out to creditors, it is the trustee who will be making those payments. In a chapter 7, there is usually not a payout to creditors, but in a chapter 13, there usually is.
If a creditor wants to get paid, then he must file a “Proof of Claim” with the court, which says how much he is owed, whether the debts is secured/unsecured, priority/nonpriority/etc. Here is a link to the standard form, with an explanation on how to fill it out.
In a chapter 13, if you are a creditor, you ALWAYS want to file a Proof of Claim. Even if it looks like there will be no payout, things change. The debtor may have a huge tax refund or a large inheritance, and you won’t get paid unless you file by the deadline.
In a chapter 7, if you are a creditor, you probably DO NOT need to file a Proof of Claim. The only exception is when the chapter 7 trustee mails you a Trustee’s Request for Creditors to FIle Claims. This means that the chapter 7 trustee has discovered some kind of asset that he can sell off and use to pay a portion of money back to the debtor’s creditors.