How does a collection agency go about filing a lawsuit against you?

If the agency is an asset buying agency, the debt is owed to them so they follow your county procedures for a suit...getting a case number, filling out and filing of the summons and complaint, service of the summons and complaint, affidavit of military service...see you in court.

The save follows for non-owned debt except first they will validate the debt and get suit authorization from the original creditor.