Don't know what part of Italy you will be traveling to, but in general, lines at the ticket station can be long and slow. You should use the machines to buy your ticket, but you generally need a credit card with a pin number. Some machines take cash (euros), some don't. I've seen situations where there is no salesperson at the station, just a machine, the machine would not accept cash, and the person didn't have a pin number for their credit card. That can be bad.

Depending on which train you are on, local or not, validate your ticket by inserting it into a yellow machine before boarding, or else face up to a 200E fine if caught on board. A ticket with a date and assigned seat doesn't need to be validated, just local trains without an assigned seat.

In some cities if you are using the machine to buy a ticket at the station, someone will come over and start helping you, like it or not. Tell them you don't need any help because when they finish they will expect a tip and give you bad looks if you don't cough it up (note, I've only seen this in Naples, where someone also may also offer to help you bring your luggage down off the train then start giving you menacing looks if you don't give a tip.).