Yes, you have to indicate some information, e.g. from, to, date, time. When you see the timetable, choose a journey and click the red button, where it says “from XY swiss francs”.
If you are on a laptop, perform as follows:
1. Visit https://www.sbb.ch/en/buying/pages/fahrplan/fahrplan.xhtml
2. Enter from, to, date, time and “search for connection”
Pro tip: The trains “IC81” are operated directly between Zurich airport and Interlaken, departing Zurich airport.45, for example 10.45am
3. Press the red “from CHF 34.40”
4. Make sure, the travel options are as follows:
Single journey, 2nd class, full price, point-to-point-ticket
5. Click continue, and enter your personal information and fulfili the payment via credit card or another payment method.