Hello Launnoachoi24
In Switzerland, we do not book a train or bus travel, we use trains and other public transport services like others use their suburban trains.
Our trains, buses, trams, boats are all mass transit, they do run every 7, 10, 15, 20, 30 or 60 minutes, depending on the line, and we simply board them whenever we like or have a need to do so. Thus, we go to the station or pier, check for the next departure (or use the SBB Mobile app to check the schedule), we get on the next service, have a ride, and get off at the desired destination. So simple. On board is free seating, you can take a seat in the respective travel class (1 stands for 1st class, 2 for 2nd class). If you want to take a seat next to someone else already sitting there, it is part of the Swiss culture to ask if the seat is still free before taking it, although it is often obvious that the seat is still free.
The Swiss Travel Pass / Flex allow you to travel at will for the entire validity day, say hop on and off as many times you like. This is the great advantage of having a day pass.
9 Oct means the start day of your pass. From this day on you can choose any date on which your pass should be valid. Consequently, from 9 Oct, you can activate your 1st day of your pass, 12 Oct.
The only trains you have to ‘book’ are the Glacier Express, Gotthard Panorama Express, and the Bernina Express if you want to have a seat in the panorama coach.
Concerning seat reservations you might be interested in reading this blog:
https://community.sbb.ch/d/23887-demystifying-seat-reservations-on-swiss-trains-a-comprehensive-guide
It is not necessary to reseve 1st class seats in regular trains, and for most trains it is not even possible at all. There are always enough seats left.
Does my explanation on the use of Swiss public transportation that make sense?
Do not obverthink the travel in our country, it will be so easy as you will see yourself once you got here.
Kind regards,
Roland