Hello gabbyrosales
Thank you for your inquiry.
It depends on what kind of train you bought. There is no seat-reservation obligatory in the Swiss trains. You are allowed to board the train with a valid ticket. And depending on the load, you may have room to sit.
If you make a trip abroad, the reservation of the seat is obligatory in most trains. If you are going abroad, I recommend you to reserve a seat in any case.
For further questions we are there for you. Have a nice day.
Greetings ZoeS