In order to contest the divorce, you will need to file an Answer with the Clerk of the Court. This can be as simple as sending a letter to the court stating that you "generally deny the allegations in the Original Petition." You will need to reference the Case Number or Cause Number, which should be found at the top of the divorce petition. Usually, the Court Clerk's address is listed on the service of citation form that you should have received from the process server. You basically have 20 days from the date your were served with the petition, to file your Answer.
A word of warning: contested divorces can be tricky, especially if they involve children. You are expected to follow all court rules (just like a lawyer), even if you represent yourself. Therefore, you might be better served to hire a lawyer to help you, including filing the answer,
