Action required for a summons?

I received a summons at my house, signed for by a visiting relative at my house. What am I required to do?

It says" you are hereby summoned to answer the compliant in this action and to serve a copy of your answer, or, if the complaint is not served with this summons, to serve a notice of appearance, on the plaintiff's attorney within 20 days after the service of this summons, exclusive of the day of service; and in case of failure to appear or answer, judgement will be taken against you by default for the relief demanded in the compliant"

Background: My divorce attorney wants the remaining fee for her services. However, I am withholding 15% because the split of asset 401k funds has not been done. As a sidenote, I believe I was poorly represented and the fees were excessive for what was actually done.

What exactly am I required to do if anything. Write a letter explaining my position? Show up for a for?

Thank You