The filing of a bankruptcy petition creates an automatic stay. This is basically like a stop sign and tells your creditors that they are no longer free to bring any further proceedings against you or your property. Almost any type of actions that you can think of are stopped, such as a lawsuit, collection efforts, etc. The automatic stay operates with respect to any claims that came about prior to the filing of your petition.
Even though the automatic stay prevents most actions, the Bankruptcy Code provides numerous exceptions where the stay does not apply. A creditor can file a motion for relief from stay. This is asking the Court to grant them an exception and to allow proceedings to continue against you. Generally, the only type of creditor that brings a motion for relief from stay is a secured creditor, such as a mortgage company or automobile lender. However, there are even ways of getting around this type of situation.
Basically, the stay provides the debtor with the opportunity to exempt his property and to obtain what is known as a "fresh start".