If you have received a complaint and summons in the mail from the Small Claims Court then you have been sued and you are a defendant. The Complaint contains the claims against you.
The Summons contains the date you must appear in Court.
You do not need to file anything before you appear in court. If you do not appear in Court on the date listed in the Summons, then you risk losing the case.
If you are a defendant and have a claim against the plaintiff, you may file a counterclaim. There is a filing fee to file a counterclaim.
A counterclaim filed in the Small Claims Court is also limited to money damages of $6,000. You must file the counterclaim at least seven (7) days before the trial.