The main part of Perl is the interpreter. The interpreter is available for Unix, Windows, and many other platforms. The current version of Perl is 5.005, which is available from the Perl website or any of a number of mirror sites (the Windows version is available from Activestate. The next release of Perl will be version 5.6; the jump in version numbers is because it was felt that the number of additional features between releases warranted a larger difference between version numbers.
Along with the interpreter come the manuals for Perl. These are accessed via the perldoc command or, on Unix systems, also via the man command. More than 30 manual pages come with the current version of perl. These can be found by typing man perl (or perldoc perl on non-Unix systems). The Perl FAQs (Frequently Asked Questions files) are available in perldoc format, and can be accessed by typing perldoc perlfaq
Watch while this is demonstrated; you'll get a chance to try it soon.
Perl also comes with a collection of modules. These are Perl programs which carry out certain common tasks, and can be included as common libraries in any Perl script. Less commonly used modules aren't included with the distribution, but can be downloaded from (CPAN) and installed separately.