If you've been served with a petition for dissolution of marriage, you need to file an answer within the time frame allotted by statute, which is considered 20 days. You would review the petition, which is enumerated and you would specifically admit or deny the allegations identified in each of the enumerated paragraphs.
If you deny one of the factual allegations in one of the enumerated paragraphs, it is recommended that you expand on that, why are you denying that allegation. Make sure that you have gone through the entire petition and either admitted or denied or indicated that you do not have the knowledge to answer that particular enumerated paragraph. Once complete, you would sign it and file it with the court.