A custom module can be created for code that needs to be used in numerous Perl scripts. As a sort of silly but easy example, let's say you want to print a welcome message at the beginning of each of your Perl scripts. First, create a module.
~]# touch /usr/share/perl/modules/foo.pm
In the module, add your welcome message, such as "Welcome to my Perl script."
#!/usr/bin/perl print "Welcome to my Perl script\n";
Here is how you would use the module.
#!/usr/bin/perl use strict; use warnings; use lib "/usr/share/perl/modules"; use foo;
Now, when running your Perl modules, "Welcome to my Perl script" will be printed to the console.