I hope you're not confused between package main and Main. The former is automatically provided by Perl and each Perl program are implicitly in a package main. The later is normal user-defined package name.

Package Main::Contact indicates nothing about inheritance between Main and Contact, the double colon ("::") notation indicates physical structure where Main is the directory under which the file Contact.pm is located (it doesn't mean though that Main.pm doesnt exist).

About the layout.... I get used to put my private Perl modules under directory lib as found in CPAN module distributions (e.g. CGI-Application-x.yy/lib/CGI/Application.pm). You may also use lib/perl as seen in the standard Perl module directories layout by the system (e.g /usr/lib/perl or /usr/lib/perl5). If there are more sibling directories (as in my case), they are all under single directory (e.g. myappl) so later I can say,

use lib '/path/to/myappl/lib'; # or
#use lib '/path/to/myappl/lib/perl'; # whichever the case
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