Once to "Roma Fiumicino" airport, have the Leonardo Express Train to reach "Roma Termini" railway station.
Leonardo Express train runs twice an hour and it takes more or less half an hour.
Once to Roma Termini, look for a train to Cassino (it takes more or less 2 hours). The train timetable can be looked up at the following website: www.trenitalia.it
In the station there are automatic ticket machines or you can buy your ticket at the ticket window.
You can also reach Cassino by train from the Naples railway station.
Once to “Capodichino airport” in Naples, have a “Alibus” bus to reach the railway station (Napoli Centrale in piazza Garibaldi).
Validating your train ticket.
Before your board any train, place your ticket in one of the yellow validating machines. Tickets may be purchased in advance but are good only for the day that you validate it.