I started this thread wondering more about the How-To's for train tickets than the Which Ones.
Which one is a little complicated and a lot of math. The how to isn't so bad though.
There are no ticket gates at the stations- train, bus, what have you. There are ticket vending machines, you can get your tickets there for point-to-point travel. Zurich Airport-Wengen was on my mind, that would be 1 ticket and around 5 different changes. You use the 1 ticket for the entire trip.
The vending machines would not accept my American credit card, so I had to buy the ticket from a human at the ticket office and sign off on it. ( The self-checkout machines at COOP also would not accept my American credit card. Everywhere else was fine.)
A ticket inspector will be on the trains asking to see your ticket on each leg of the journey.
Generally the tickets are not tied to a specific departure but valid for a certain period, i.e. use sometime that day.
There is an app for this. I used the app as well, SBB. Starting it up is a little confusing because tourists are not the target customer for the app, you have to poke around a bit to find the Half Fare Card and Swiss Pass for visitors. (I forget where but there is a section for Overseas Visitors (?)) There is a TIMETABLE button on the app, no BUY button. As you look at the timetable the option to buy a ticket will pop up. The ticket shows as a QR code. You can add users to the same app. As long as you stay together that part works out fine.
I had the Half Fare Card. A QR code for it in the app and a paper print-out. I presented it to every conductor, sometimes they seemed happy to see it, other times it felt like they didn't really care about it.
All the staff were proficient in English and very friendly and helpful.