Current Perl documentation can be found at perldoc.perl.org.
Here is our local, out-dated (pre-5.6) version:
The standard release of Perl (the one maintained by the perl development team) is distributed only in source code form. You can find this at http://www.perl.com/CPAN/src/latest.tar.gz, which in standard Internet format (a gzipped archive in POSIX tar format).
Perl builds and runs on a bewildering number of platforms. Virtually all known and current Unix derivatives are supported (Perl's native platform), as are proprietary systems like VMS, DOS, OS/2, Windows, QNX, BeOS, and the Amiga. There are also the beginnings of support for MPE/iX.
Binary distributions for some proprietary platforms, including Apple systems can be found http://www.perl.com/CPAN/ports/ directory. Because these are not part of the standard distribution, they may and in fact do differ from the base Perl port in a variety of ways. You'll have to check their respective release notes to see just what the differences are. These differences can be either positive (e.g. extensions for the features of the particular platform that are not supported in the source release of perl) or negative (e.g. might be based upon a less current source release of perl).
A useful FAQ for Win32 Perl users is http://www.endcontsw.com/people/evangelo/Perl_for_Win32_FAQ.html