Are réservation in Swiss trains necessary ?

do l need to have a seat # ?

Do l have to pay a supplement to use trains in Switzerland ?

what are some of the train names in Switzerland ?
what is the Swiss Travel Pass ?

Reservations are mostly not necessary in Switzerland, and not possible most of the time

If you want to sit in the Panorama Car on the Bernina Express or Goldenpass line, then you need to pay a reservation fee, but you can always sit in the unreserved regular cars. The scenery is the same!

The only domestic train with compulsory reservation is the Glacier Express between Zermatt-St Moritz, but you can take regular trains along the same route.

International trains to France and Italy do need reservations.

The Swiss Travel Pass gives access to a few more mountain railways than the Eurail pass, and includes buses and city transport, but it's more expensive.

There's some really good information, including passes and named trains, here

https://www.seat61.com/train-travel-in-switzerland.htm