The Swiss Travel Pass serves as your ticket, and it is unnecessary to purchase additional tickets where your journey is fully (100%) covered by the Swiss Travel Pass. It allows you to get on and off public transport services at your leisure.
For mountain transport, where the STP often grants a reduction only, you can easily get them from the stations’ ticket office. Simply mention that you hold the Swiss Travel Pass.
Swiss Travel Pass – the All-in-one-Ticket for Switzerland | SBB
Kindly note: using the Swiss Travel Pass you must always have your physical passport or ID with you (copies / photo copies are not accepted) and show it whenever asked by the ticket inspector.