"An .so file is a compiled library file. It stands for ""Shared Object"" and is analogous to a Windows DLL.
Often, package files will place these under /lib or /usr/lib or some place similar when they're installed. If you extract an .so file to a location in your $LD_LIBRARY_PATH, a program that requires the library should be able to use it.
Ideally, read the accompanying documentation to ensure that it's in the right location.
If you run a command like locate adobe-flashplugin from the Terminal you may see some existing similarly-named libraries."