Rahul, do you have access to a good library and/or to interlibrary
loan? If so, just visit the section with any jewelrymaking books and
look up polishing and buffing in each one, until you find something
that looks possible for you. Only in newer books will you find
on tumble-polishing. Most earlier will be on
hand-polishing (tedious but sometimes necessary) and polishing using
various wheels on a bench grinder or other polishing machine.
Judy Hoch (of this list) has an affordable book on tumble-polishing,
available in most catalogs (like Rio Grande).
All the best,