This varies an awful lot per country, per traincomp and per kind of train. Trains are not planes. Even in 1 car there may be different layouts in various parts. There are no seatbelts and no stewardess to give instructions etc. so you can sit/stand/ whatever you like. Also never no tipical USA style treat all pax like ignorant kids and unable to think for themselves.
For the tipical overloud USA: most railways also have quite decent SILENT cars where it should be as this name says. The rest is free to do what you want-but playing music etc that other can hear is never ever allowed. Screaming in your fone so that anyone thinks you would not need that fone at all is also ´frowned´ at.
USA also seem to be brainwashed to believe it should be 1st, also nonsense. In fact 1st cl passholders are known in many countries to be quite a nuisance to the existing bisnis people (or more often govt officials) who get enough expense paid to be able to use it. Besides a wider seat 1st does not give more extraś-except in GB.