The configuration and type of seating you'll find when you get on a train in Europe can vary quite dramatically from one country (or one train) to the next. You may encounter an arrangement that differs from the examples below, but we hope that this information will help you find your seat more quickly.
To find your seat number, first find the correct car number indicated on the outside of the car. Then make your way down the aisle until you see your seat number. Numbers are displayed above seats in a similar fashion to those on airplanes.
On some train cars, many of the seats are facing each other, with a small table in between. Ticket vendors assume that, for instance, a couple traveling together will want to sit across from one another. The numbers for the seats are usually consecutive for adjacent seats, however, so when you look at the reservations for you and your partner's seats it may look like you're not sitting together. You are - you're just sitting across from each other. The numbering system for this reason can be a cause for confusion even before you get to the train platform - especially if you're traveling with another person or in a group.
If you'd prefer adjacent seats, make that clear to the vendor at the ticket counter beforehand. Note that ItaliaRail cannot change seat assignments, as right now they come automatically from Trenitalia. You can attempt to change them at the station prior to getting on the train, assuming there are open seats to which you can be moved.
The same potential confusion exists with sleeper compartment bunk numbers, too, so don't worry if the numbers for you and your partner appear to be in different compartments. When you book two seats or bunks at the same time, the assumption on the part of the ticket seller is always that you want to be together. Confirm or clarify if it makes you feel better, of course.
Some trains require seat reservations, and on other trains it's optional. If you're riding a train on which reservations are only recommended or completely optional and you don't have a reservation, you can sit in any available seat in the appropriate class you have booked.
Note that in these trains there is often a spot for reservations to be posted at each seat, even if the seat is reserved for later in the trip. If your journey has you getting off the train before the reservation's starting point, then, you're welcome to take that seat.
In an open-saloon style car, seats are clearly numbered once you get on the train, usually overhead (similar to where the numbers are on an airplane). The aisle seat is often depicted with a person standing next to it, and the window seat with a rectangle representing the window.
Some open-saloon cars also have bench-style seating as opposed to individual seats. In this case, they're typically not reserved, so you can sit wherever you like.
In compartments, numbers are typically on a diagram outside the door of the compartment, and may also be inside at each seat (but don't count on it).