Are you the named defendant/respondent to the civil action?
NO, I AM NOT A DEFENDANT/RESPONDENT:
In Washington, a civil action is commenced by (1) service of summons and complaint, or (2) by filing a complaint (normally, the moving party will do both simultaneously). Assuming the summons was properly served (another legal issue), you must appear. Notify the court ASAP if you cannot appear.
YES, I AM A DEFENDANT/RESPONDENT
The summons should have come with a complaint. The complaint must include the jurisdiction and venue, a factual statement, right to relief, and the relief requested. You must answer the complaint. The answer is normally due within 20 days after service of the summons/complaint. The answer may include a general denial of the allegations, affirmative defenses, etc. Your answer may also move for dismissal for lack of jurisdiction, insufficiency of service, failure to join a party, or failure to state a claim upon which relief can be granted.
If you do not respond to the summons/complaint (fail to appear or answer), the moving party (plaintiff) may present proof to the court that you failed to appear. They may also make a motion for default judgment, which may be enetered immediately or any time after the entry or the court's finding that a party is in default. If the amount of the judgment is for a known, specific amount, the court may award such amount. If the amount is uncertain, the court may order hearings or other procedures to determine the proper amount of damages.
In short, give your best efforts to honor the summons.