How do you answer a civil summons for a lawsuit?

Answer each side -plaintiff and defendant- send one another interrogatories.

Try this link for the links to get the forms to answer the lawsuit. Often the Court Rules REQUIRE that you be served with the Response form when you are served with the Summons and Complaint.

Answer

This is more complex than you have actually explained on the board, so I suggest you seek out legal counsel. This is also advisable because the precise mechanism for responding may differ by jurisdiction, and it is therefore difficult to generalize in a forum such as this.

However, that said, if you are going to answer the complaint (rather than, for example, file a motion to dismiss or other pre-answer motion), you generally will want to respond to each numbered allegation of the complaint (the allegations usually appear in separately numbered paragraphs). The responses are generally "admit" or "deny" in nature, although it is usually permissible to "deny for lack of knowledge" if the circumstances dictate.

Once the admissions/denials have been made, one often assets any applicable "affirmative defenses", again, in separately numbered paragraphs. Some may include:

The plaintiff/complainant fails to state a claim against the defendant upon which relief may be granted. (Meaning the debt is not valid or at least the plaintiff has not plead it clearly).

If the defendant is indebted to the plaintiff he/she is also indebted to ....(Meaning there are other parties involved which were not named as plaintiffs).

The right of action set forth in the complaint did not accrue within the time set forth by the laws of the defendant's state. (The state's SOL for the action has expired).

It is best for the defendant who is representing themselves to respond with their own wording, as judges tend to be more lenient in Pro Se cases.

There may be other applicable affirmative defenses, but these are dictated by the basis of the cause of action being asserted by the Plaintiff. An affirmative defense is, by nature, a legal or factual "avoidance" of the claim, and to that extent differs from a mere denial of the allegation.

It is critical that the answer get filed with the Clerk within the time allowed by law (usually specified on the Summons), and that a copy get mailed or delivered to the Plaintiff or his/her/its attorney. The failure to get an answer filed when required may result in the entry of a default, such that you will be considered to have admitted the material factual allegations of the complaint.