Hello azalea4va
The Swiss Travel Pass is your ticket, and you do not need to purchase additional tickets unless you want to use it on routes where the Swiss Travel Pass is not or partially valid or if you would like to upgrade from 2nd to 1st class.
Where accepted, the Swiss Travel Pass is a hop on hop off ticket. You can walk on trains, buses, tramways, and boats at will and simply have a ride. The validity map is here:
https://www.sbb.ch/en/tickets-offers/travelcards/area-validity-map.html?layers=ch.sbb.geltungsbereiche.mvp-sts
On routes where the Swiss Travel Pass is accepted, you simply show the Swiss Travel Pass paper ticket or the QR code of your e-ticket together with your physical passport (no photo copies, no images on smartphones of it).
Again, the Swiss Travel Pass is considered a valid ticket for the SBB luggage shipping service. It simply has to be valid on the day you want to ship your luggage.
Here is more information on the STP:
https://help.myswitzerland.com/hc/en-us
Here is our guide about seat reservations on Swiss trains:
https://community.sbb.ch/blog/23887-demystifying-seat-reservations-on-swiss-trains-a-comprehensive-guide
You will see that you will not find it confusing any further once you have been using it. There is no simpler ticket to use than the Swiss Travel Pass. And, you will be amazed by our public transit system and its simplicity of access/use.
Kind regards,
Roland