You file a notice of appearance which requires the other side to give you notice when they file anything further.
After you give notice of your appearance you answer the complaint, file it with the Court and send a copy to the plaintiff. in your answer, go paragraph by paragraph, and either admit, deny or deny for lack of information. When you have finished answering paragraph by paragraph, you list your affirmative defenses.
WA is a notice pleading state. You are not obligated to provide every quantum of evidence you have at this point. But they cannot default you if you file a notice of appearance.
Your local law library or the internet can help you come up with the caption and the words.