How do I install perl modules??

It depends on what you already have.
If you run on Windows XP and would like to install ActivePerl, you can follow the instructions shown in:

http://www.mathpath.net

go under Programming Languages (Perl) and under installation.

For the Perl (CPAN) modules, if you have ActivePerl installed in the default directory of c:/Perl, then use the DOS screen , do

cd c:/Perl/site/lib

followed by ppm

You will see a PPM> prompt from which you can get help by typing help.
To search for a particular subject, do
search <subject>, for example
search cpan
the first token of each line displayed is the name of the module that you can install, and all you have to do is to type
install <name of module>, for example
install cpan

If you run under Linux or other platforms, the proedure should be similar, but the directories may differ.
Note also that under ActivePerl, the modules available are different from those displayed under the Perl tutorial.

The following link includes many useful documents worth reading:
http://www.perl.com/pub/q/documentation

from which the installation of modules is further documented in:
http://search.cpan.org/dist/perl/pod/perlmodinstall.pod