Hello OZ59
By the number of questions we do receive concerning seat reservations, no, it does not seem to be clear to everyone visiting our country. Nevertheless, the SBB Community is the right place to ask this question.
You can find the answer in another thread were I have answered the question already. May I ask to check the link below. And, we will soon publish an FAQ with the most asked questions regarding seat reservations.
https://community.sbb.ch/d/23170-purchased-a-sbb-6-day-1st-class-rail-card-cant-reserve-tickets/4
The topic has not been in our focus so far, because we, the Swiss, do not bother with making seat reservations on trains. After reading my answer in the link posted above, you will understand, why.
Get back to us should you have more inquiries.
Best wishes,
Roland