Consider looking at perlrun and perlvar for @INC.

Also, the Perl that came with your operating system belongs to your operating system. System utilities may depend on the system Perl working properly and having exact versions of certain modules installed. Do not manually install (or "copy") files into its directories. Use your operating system package manager to install Perl modules for the system Perl.

Also see local::lib and/or App::perlbrew.

For the general process of module installation, see Yes, even you can use CPAN and CPAN resp. CPANPLUS or App::cpanminus.