Perl comes with a lot of documentation, but it takes some time till you get used to using it. In this part of the Perl tutorial I'll explain how to find your way around the documentation.
perldoc on the web
The most convenient way to access the documentation of core perl is to visit the perldoc website.
It contains an HTML version of the documentation for Perl, the language, and for the modules that come with core Perl as released by the Perl 5 Porters.
It does not contain documentation for CPAN modules. There is an overlap though, as there are some modules that are available from CPAN but that are also included in the standard Perl distribution. (These are often referred to as dual-lifed.)
You can use the search box at the top right corner. For example you can type in split and you'll get the documentation of split.
Unfortunately it does not know what to do with while, nor with $_ or @_. In order to get explanation of those you'll have to flip through the documentation.
The most important page might be perlvar, where you can find information about variables such as $_ and @_.
perldoc on the command line
The same documentation comes with the source code of Perl, but not every Linux distribution installs it by default. In some cases there is a separate package. For example in Debian and Ubuntu it is the perl-doc package. You need to install it using sudo aptitude install perl-doc before you can use perldoc.
Once you have it installed, you can type perldoc perl on the command line and you will get some explanation and a list of the chapters in the Perl documentation. You can quit this using the q key, and then type the name of one of the chapters. For example: perldoc perlsyn.
This works both on Linux and on Windows though the pager on Windows is really weak, so I cannot recommend it. On Linux it is the regular man reader so you should be familiar with it already.
Documentation of CPAN modules
Every module on CPAN comes with documentation and examples. The amount and quality of this documentation varies greatly among the authors, and even a single author can have very well documented and very under-documented modules.
After you installed a module called Module::Name, you can access its documentation by typing perldoc Module::Name.
They both are based on the same documentation, but they provide a slightly different experience.
Keyword search on Perl Maven
A recent addition to this site is the keyword search on the top menu bar. Slowly you will find explanation for more and more parts of perl. At one point part of the core perl documentation and the documentation of the most important CPAN modules will be also included.
If you are missing something from there, just make a comment below, with the keywords you will looking for and you have a good chance to get your request fulfilled.