The First Judicial District Court Clerk's Office has posted Instructions for Preparing, Filing, Serving an Answer in Justice Court on its page of Justice Court forms. (There are sample District Court forms as well, although no Answer as of this posting.)
NOTE: This document has been prepared as a courtesy and to assist you with completing your Answer. It is not to be construed as providing legal advice or representation on how to prepare your case or defense.
If you've been served with a Summons and complaint in the Justice Court and have been named as a defendant in the case, you have the option of preparing, filing, and serving an Answer in response to the complaint. An Answer is your formal reply to the court and the plaintiff's attorney (or the plaintiff if he doesn't have an attorney.) You must reply to each paragraph/allegation in the complaint by admitting it, denying it, or denying it because you don't have enough knowledge or information to be able to admit it. You only have 20 days from the day you were served with the Summons and complaint to file and serve your Answer. If you don't file an Answer in the court and serve a copy to the plaintiff's attorney (or the plaintiff, if he's unrepresented) within 20 days of the day you were served, then the plaintiff may obtain a default judgment against you.
WARNING: The filing of an Answer affects your legal rights. If you file an Answer, you have agreed that the court in which you file your Answer has good and proper jurisdiction over you to decide your case.
If you are in Reno, there is a sample Answer on the Reno Justice court civil forms page. In Las Vegas, the Clark County Civil Law Self-Help Center has information on civil actions including what to do if you've been sued, as well as small claims actions.