The line use Crypt::Blowfish; will look for and load an optional module. This module needs to have been downloaded and installed on your machine. Many modules are only Perl but Crypt::Blowfish is probably an example of a module that has a binary component.
in reply to PERL And Blowfish
Since Perl comes from a UNIX background, it is assumed that UNIX tools including a compiler are available to you. Windows users can also install these tools or make use of pre-packaged distributions.
My recommendation if you are starting out with Perl is to install the ActiveState distribution since this is well known and has good support for downloaded packages. You will need to learn how to use the PPM (Perl package manager) tool that is used to find and install modules.
I have added the University of Winnepeg repository to my PPM configuration since this has better support for the Crypt:: modules.