First, some advice. See the Atac website (click on the British flag). It has some useful — albeit creatively phrased — explanations. As for the warnings, it’s pretty simple. Once upon a time (until around 1980), urban buses and trams had ticket-sellers on board. When that ended, the country went to system of pre-purchasing. You buy, put it through he machine on the bus, and show it to an inspector if he/she boards (which is more frequent these days). The problem is where to get the tickets. The answer: Local tobacco shops (big “T”) and some, not all, newspaper kiosks. If you’re staying in a city for a week, best to buy 20 or fork out the money for a monthly pass (tessera). If the machine doesn’t work, Ok. Don’t fret. Hold the ticket and show the inspector. They know the drill with malfunctioning machines. They also know you can’t stamp the ticket if the bus is packed. Obviously, if someone wants to hassle you, they will, but that’s a personal choice and not a reflection of some big bad system. Again, bottom line, buy a bunch of tickets (usually at €1 each) the first chance you get, so you dodge the issue. Fines run between €100 and €500.