You, you install those modules. There are several ways, depending on which OS your server is running.
The universal way to do it is to run "sudo cpan" (run cpan as root). A console shows up, you may have to answer some questions if this is the first time you run cpan (just keep pressing enter). When it's done, type in "install Net::IRC" and it will download all the files and dependencies, compile and install them for you.
If for some reason you cannot use cpan (these things happen), then you can use your OS's package manager. On RedHat/CentOS it's yum install perl-Net-IRC, on Ubuntu it's apt-get install perl-Net-IRC. The name of the package to install is almost always perl-Name-Of-The-Package-Separated-By-Minuses
If you use Windows and ActivePerl, then you get your own package manager which works similar to cpan.
So installing new perl packages is easy, but you need sudo access.