I was served with child support papers in the state of florida and need to write a response to the court. What should this letter include?

You do not write a letter to the court, you must file an appropriate pleading called an ANSWER.  You can obtain the forms to file an answer at the clerks office or possibly download them on line. There are instructions with the family law forms and you must be sure to follow the instructions and sign the pleading. The pleadings must be filed in the court listed on the top of the papers that you were served with, and a copy sent to opposing counsel. Be sure to keep a copy for yourself of every thing you file. There are lawyers at most court houses that provide low cost advice on how to complete the forms. You answer must address all the allegations in the petition by either admitting or denying each allegation.