Generally, a motion for summary judgment means the party is trying to obtain a judgment by arguing that there are no questions of fact, and that if the law is applied to the facts, they win. To respond, you have to raise a question of fact by affidavit. For example, you have to produce evidence, in an affidavit, that the debt is disputed, that the amount is not correct, that they don't own the debt, etc.
Generally, a motion for summary judgment comes after someone is served and has filed an answer. If you have not filed an answer, you can deny filing an answer in response to the motion for summary judgment.
However, I'm not familiar with WA law, and a motion for summary judgment there may be different.
You might want think about getting a lawyer - motion practice is a bit more tricky than filing answers, and procedures (when, how, the form of affidavits) becomes important.