Welcome. First thing you should know is that you can play as a driver or as a dispatcher. The second one is unlocked after driving 400km as the driver so I will not describe it there, because you will take a little grasp of dispatcher role when you play as a driver. Firstly, you should read basic rules of polish railway, which can be found here
https://wiki.td2.info.pl/index.php?title=Instrukcja_Train_Driver_2_(instrukcje_kolejowe) It's very simplified, but sadly you will have to try and read it with google translate and ask somebody in case you will not be able to understand something. Then try to operate one vehicle in singleplayer. sn81 and sm42 are probably easiest to operate. You can find cheatsheet of keys here
https://wiki.td2.info.pl/index.php?title=Klawiszologia under "Maszynista" and "Sm42" headlines. When you will be able to accelerate and decelerate properly, you can try multiplayer. Most players try to communicate in English if there is a foreign player. In multiplayer you simply get a timetable from the dispatcher, who is responsible for one scenery, and drive between sceneries following rules.