It depends upon which train you'll be taking. Be aware there is a few InterCity ("IC") or the ICPlus trains that are a bit quicker & make fewer stops .... going via the IC it's a 59 minute ride between Rome and Orvieto, and the stations are Rome Termini, Orte and then
your destination, Orvieto. It sounds like you're planning to take the slower regional train (1 hr, 18 min), then it's: - Rome ...