If you are served with a family law Petition (dissolution, parenting plan, child support modification, etc.) within the State of Washington, you have 20 days to file a "Response" to the Petition. If you were served outside the state, you have 60 days to file your "Response."
If you are served with a family law motion, your response time will depend on the local rules of the court.
In drafting a Response to Petition or a response to a motion, it is best to have an experienced attorney draft these documents. Often, there are specific legal standards that must be met in a particular case. As the responsive party, it is your job to frame your arguments so that they meet the legal standard. It is often difficult to do this on your own.
So, when you get served with legal paperwork, read the pleadings and then call an attorney.