If you were served with a Summons and Complaint, you should first record the date and manner in which you were served, and then retain a lawyer to file a timely response on your behalf. In most instances, for Superior Court lawsuits, you have 30 days from the date of personal service to respond to the Summons and Complaint.
In the event you absolutely cannot afford an attorney to defend you, you can represent yourself "in pro per". You would file either an Answer or a General Denial, and pay the first appearance filing fee.
The form for the Answer is (Judicial Council Form PLD-C-010):
The form for the General Denial is (Judicial Council Form PLD-050):
If you cannot afford the first appearance filing fee, you may apply for a fee waiver. See:
The information presented here is general in nature and is not intended, nor should be construed, as legal advice. This posting does not create any attorney-client relationship with the author (who is only admitted to practice law in the State of California). For specific advice about your particular situation, consult your own attorney.
You need to file an answer to the complaint. Ask the self help center at the court for help. you will check thr box marked general denial and include some affirmative defenses such as statutes of limitation. Contact a local litigation attorney.