Generally speaking, Italian trains are divided into three categories: Regionale (R), Intercity (IC) and EuroStar.
Among the three categories, R is the slowest, the carriage condition is the worst, but the fare is the cheapest. Trains stop at every station, fail to report, and are often late. After the delay, we have to make way for more advanced IC and Eurostar, so R is really slow, but it is also a good way to get familiar with local customs. Another point is that although R's car is in bad condition, it is sometimes divided into 1 and 2 cars. Never let the ticket seller find fault with the wrong carriage.
IC is a kind of train centered on all aspects. Its speed is not the fastest, and the interior environment is not the best, but the conditions in all aspects are better than R (local train). Sit down on the IC, or other passengers will protest to you. The stops are similar to domestic express trains, only stopping in some big cities. In most cases, the station will be reported.
You must have heard of Eurostar. The conditions in the car are slightly worse than those of the domestic Harmony, but the speed is not much slower. Eurostar, like IC, should sit down according to the seat number on the ticket. The stops and IC almost only stop in big cities, and each stop will announce the station. In addition, Eurostar has the highest driving level in Italy, so the probability of being late is also the lowest among the three types of trains.