Open a Terminal window. Type  perl -e 'print "Hello World!\n";' That's a complete Perl program. You've just started. :)

Go to the recently added How Do I Use Perl Monks? Read. A lot.

Specifically to OS X, I've put an icon for Terminal in my Dock. The Terminal is how you interact with the Unix underpinnings of the New Mac OS, and Perl lives in the Unix part of Mac OS X. You can have more than one Terminal open at once, you can save Terminal arrangements (number of windows open, size of windows, font used, font color, background color, etc.), you can customize the living daylights out of the Terminal.

Get a Perl book. I'd recommend the Llama, or Perl for Web Site Management. See the Book Reviews section.

Enjoy. This stuff is supposed to be fun.

Update: I didn't notice that you asked this Anonymously. You should also join The Monestary. You can get a lot out of our little corner of the universe. At the very least, it let's you customize how everything looks.

$ man perl
[download]

$ perldoc perl
[download]

-- Can't never could do anything, so give me and inch, I'll make it a mile.