Russian trains can be subdivided into three main categories:
Firmeny train (фирменный)
Firmeny trains are privately run Russian trains offering high quality service with higher prices as well. Each train has a specific interior design based on the operator. Some cities have their own original trains that they are quite proud of and try to make as comfortable as possible - these trains typically have names such as Kama (a train run by the city of Perm). The train numbers for Firmeny trains consist of a zero followed by 2 numbers and one letter. For example, train 002M "Rossia" Moscow-Vladivostok is a Firmeny train. These trains typically have 1st, 2nd and 3rd class compartments and have a restaurant car. Russian Rail sells Russian train tickets on all Firmeny trains.
Express train (скорый)
Are quite good, fast trains however they are a bit less comfortable than Firmeny trains and usually make a few more stops. They usually serve long distance routes and are quite popular with travelers. Like the Firmeny the number consists of a zero, 2 more numbers and a letter. The trains run regularly. Russian express trains have 2nd and 3rd class compartments, a restaurant car and sometimes a 1st class compartment.
Regular train (пассажирский)
This train stops at every station along the route so it really takes a while to get where you want to go on these, however, these trains offer a great opportunity to see Russia SLOWLY!!! The number consists of 3 numbers and a letter.
Other types of specific trains:
Electric suburban train (пригородный)
These are those green trains that run on electricity and connect large and provincial cities with their suburbs and outlying rural regions. They are pretty rickety, have funny wooden seats typically and aren't the most comfortable form of transport. And, watch out, on the weekends and whenever the weather is nice they get packed. You won't find a seat. Russians like to go to their dachas (summer houses) and most of these trains are the best way for them to get their. Tickets are cheap and can be purchased at all the Russian train stations.
Types of compartments
1st Class (SV)
First is the most comfortable and expensive option: the SV ticket. This is a first class compartment for only two people and contains two lower couches that convert into beds and a table next to the window. Also sometimes on some Russian trains which run a long journey there are showers in those SV compartments that also adds some comfort to your journey. If you would like to travel by yourself there is a possibility to buy two tickets for the couches at the same compartment. So this could be almost the VIP traveling.
2nd Class (coupe)
The next option is a less expensive class (2nd class) that is organized in compartments, each of which contain two lower and two upper berths. These are called coupes in Russian. Just like an SV, coupes have a door which locks from the inside, and thus privacy between the four people is kept inside the compartment.
3rd Class (Platzkart)
The next class is cheaper still and is called Platzkart in Russian (3rd class). This means that the entire wagon is open and there are no closed compartments or curtains. There are two lower and two upper berths, a small and narrow corridor and another two berths that are located on the opposite side near the window. So instead of a compartment there are six berths and no doors, thus there is no possibility to lock anything or for people to have any privacy. Platzcart tickets are convenient tickets if you have a short journey or if you are not interested in comfort but want to save money. In some cases, traveling by Platzkart is more convenient for a woman taking a journey by herself. In this case, the woman avoids the possibility of getting stuck in a compartment with 3 strangers. If you travel to the very south of Russia during the mid-summer months, this might be a more comfortable option because the wagons tend to get very humid and stuffy and Platzcart cabins have better ventilation and therefore may be cooler.
The last option for Russian train tickets are just seats. These are, simply put, similar to the kind of seats you will find in airplanes, and they are just as comfortable too - most long distance trains do not have seats. You can travel in a wagon with seats only for a short distance, afterwards it can become very uncomfortable but this is the cheapest option. Between Moscow and St. Petersburg there are a few trains, which have wagons with seats with different levels of comfort. Some of these trains are expensive and run for about six hours, some travel about ten, but the tickets are the cheapest. So as you can see there is a big variety of traveling options, when traveling by train - you just have to decide what is most convenient for you. Some trains such as Helsinki - St. Petersburg and Moscow - St Petersburg have very comfortable seats.