When Perl “looks for a package,” it refers to a “@USE list” and marches down that list in-order.

As you'll see from the Perl documentation (and I don't mean that as “RTFM!”) there are several ways that the content of that list can be influenced.

Also, when you use CPAN, there are a set of settings (accessible via o conf which determine where CPAN looks, what settings it uses, where it places files, and so-on.

You can, in fact, influence everything about Perl. One of the most-common situations where you do that is when you're deploying Web-server packages ... “you don't own the hardware,” and “every one of your customers' web-sites are different.” Perl can handle this quite easily. You tell CPAN to install into a site-specific location, and you (e.g. via the PERL5LIB variable...) tell Perl where to look.

But hey, we all admit it, “it's not immediately obvious how it works.” Perservere. And ask questions here... freely. You're among friends.