if you have booked with ryanair, you will find a link on their website for bus transfer in rome. this bus will drop you at the main train station.
"FROM CIAMPINO AIRPORT TO ROME" Terravision operates a direct coach service from Ciampino Airport to Rome city centre. Coaches depart from outside the departures terminal. High departure frequencies, in line with FR flight arrivals and departures. Journey time is approximately 40 minutes and cost is €4 one way and €8 return. BOOK NOW your transfer to Rome AND SAVE!
we used viator . They were waiting at the airport on our arrival and left us at our hotel and picked us up from our hotel and returned us to the airport for our return flight.