suresh_bhat
Check the legend of those symbols and acronyms:
GR means reservations mandatory for groups, not for individual travelers.
If your ticket is not a Supersaver ticket, it is valid all day so you can hop on/off as you like.
Sliding windows are only available on older coaches without AC. For a reliable answer regarding your travel date, you might want to contact the railway operator Rhaetian Railways on rhb.ch
On the Bernina Express, hopping on again is possible only on the few non-panorama coaches.