Locating libraries

[BROWNH]

When an application says it needs libraries such as Xext and m, which are
unfamiliar to me, I'm faced with the problem of knowing whether they are
installed (in RH 5.2), There are various places where libraries are kept,
and so I wondered if there was some efficient way to ascertain whether I
presently have a library on HD. If I find I need a library, is there a
special place to find such specialized libraries on line?

Haines Brown