For an indepth explanation of Perl data types see the Chapters 3 and 6in the book ``Advanced Perl Programming'' by Sriram Srinivasan.
And of course the ``Programming Perl'' by L.Wall, T. Christiansen andJ.Orwant (also known as the ``Camel'' book, named after the camelpicture on the cover of the book). Look at the Chapters 10, 11 and 21.
The Exporter, perlvar, perlmod and perlmodlib man pages.