Just go to the SBB (Swiss Federal Railways) site: http://www.sbb.ch/en/home.html
and enter Interlaken Ost to St Moritz via Brig and Andermatt (but you probably aren't actually starting from Interlaken, so enter where you are actually starting from); plus date and a time (for example 08:00). It will list all the trains. The Glacier Express will be listed as 'GEX', and it will have fewer changes than other options, and it will have an 'R' in a box, indicating reservations required.
But, there will be other options taking the same route, with more changes, and you will see the same mountains out of the window whichever train you take.