By citation, I assume you mean a Summons and Complaint.  The Complaint is the lawsuit. You will need to file an Answer to the Complaint.  If you don't have an attorney, at the law library look for Answer to Complaint in the index of Pleading and Practice.  That will give you the format for an Answer to a Complaint and will give you sample answers.  The Answer to the Complaint denies the allegations in the Complaint.  At the end of the Answer, is the Verification.  The Verification  is signed under penalty of perjury and attests to the veracity of your statements in the Answer.  You will need to file with the court, the Answer to the Complaint with an attached proof of service.  You can use a court form proof of service or you can write your own.  The proof of service just verifies the date of mailing of your Answer to the opposing party ( creditor)or the opposing party's attorney. If you write your own proof of service, it would just say that you are over 18 and the attached documents were sent via first class mail unless specified otherwise to _________ (name and address of opposing party or opposing party's attorney) on _________ (date).  You sign the proof of service under penalty of perjury.  The date you sign the proof of service should be the same date it is mailed and the same date you file it with the court.  If you can't afford the court filing fee to file your Answer to the Complaint, you can complete a court form which allows you to waive the filing fee.  The court clerk can provide you with that form.If you don't file an Answer to the Complaint with the court before the 20 days to respond elapses, you will lose by default.  If that occurs, you will need to file a motion to have the default set aside.