What can we do about our Disorderly Conduct charge?

My boyfriend and I were sitting in his car, not parked illegally, next to a public park (not in the public park). It was about 11 pm and we were just sitting in the car talking. The next thing we knew, the police drove up next to us, pointed a flashlight into the car, stepped out of their car, and asked us for ID. We are both minors, in fact, I had no photo ID on me, so I told them who I was, my date of birth, and address. After waiting 10 minutes, the officers returned to our car and told us that we would have to go to court 2 months later. They did not explain the charges, but on the summons, it stated that we were charged with "disorderly conduct 240.20 (7)." We do not believe that we did anything wrong. We are thinking about a motion to dismiss, but we do not know how to go about doing this because the police did not specify their allegations. How do we go about finding out what we are charged with? How do we go about filing a motion to dismiss? (Is it viable in this case?) We are both very scared, as we both have never been in trouble before. Any help would be greatly appreciated. Thank you.