An excellent repository of Perl documentation exists at http://perldoc.perl.org/. That's your one-stop shop. Also, szabgab has created this nice comprehensive perl index.
Your local installation of Perl comes with a full set of documentation on the Perl language and the perl execution environment. (This surprises a lot of people new to Perl.) On UNIX and UNIX-like systems (such as Linux), it's all available via the perldoc command. For example, perldoc perlfunc on UNIXy systems should give you the answer to the title question. On other OSes, Perl provides the same documentation in various forms — for example, in HTML — and with only a little searching under perl's installation directory, you should be able to find everything you need for basic questions.
If you want to link to documentation for a function, either in a node or in the chatterbox, you can do it like this: [doc://foo] where foo is the function name in question. For example, [doc://time] -> time. (Note that this also works for built-in perl variables, e.g. [doc://@ARGV])
If you want to jump immediately to such documentation in your browser, it's quite easy: simply type doc://foo (no square brackets) in the Search box at the top of any page.
(To do a general search of the documentation at perldoc.perl.org, type perldoc:// rather than doc://.)
If you happen to be viewing a PerlMonks node which contains code (such as entries in the Code Catacombs or Snippets Section), and you happen to have your Function Nodelet enabled, that nodelet will contain links to the documentation for every function used in the code displayed on the node.
If you don't mind looking at an older version of the Perl documentation, there are a couple of handy ways:
For browsing, you can visit our dusty old Library. This has an index of all the perl docs, including, for example, the Perl FAQ.
If you want info on a specific function or topic, you can type its name in the Search box at the top of any page. This will take you directly to the corresponding page in the Library.