Get a copy of "Orchestra Music: A Handbook" by David Daniels.
You can dig around online and figure out where to get it. I got my copy of the next-to-latest edition for no more than a few dollars at a library book sale when they upgraded to the latest edition.
It's probably in a college/university library close to you if you don't want to buy your own copy, as the Daniels book it pretty much the standard book on instrumentation of orchestral works.