G'day anek77713,

"Can someone give me a hint?"

One of the first tools I reach for when seeking Perl information is Perldoc. This is available online from http://perldoc.perl.org/perl.html (I recommend you bookmark this) and as the commandline utility perldoc.

"What should I read to learn building modules over existing ones?"

This is very vague: "building" (writing? creating? other?); "over" (on top of/replacing? instead of? subclassing? other?); "existing" (builtin? CPAN? in-house? other?).

Under the Reference Manual section of the link I provided above, you'll find a block of six links whose descriptions all start with "Perl modules:":

• perlmod Perl modules: how they work
• perlmodlib Perl modules: how to write and use
• perlmodstyle Perl modules: how to write modules with style
• perlmodinstall Perl modules: how to install from CPAN
• perlnewmod Perl modules: preparing a new module for distribution
• perlpragma Perl modules: writing a user pragma

One or more of those may well provide the information you're looking for. If not, please ask a more specific question.

Thnx for the answer!!!!

The problem is:

Module : Pod::PseudoPod::HTML

I wish to write a module... That will be:

Pod::PseudoPod::HTML::Book

But I can't understand how to make this...

How to link the content of Book to the Pod::PseudoPod::HTML to use the code from up the tree

Many (probably most) documentation pages have a SEE ALSO section which provides links to related documentation. The first "Perl module: ..." link I provided above ("perlmod Perl modules: how they work") has a link to perlootut - Object-Oriented Programming in Perl Tutorial. (It sounds like a tutorial is what you need.) Within that documentation, you'll find the answer to your question:

"Inheritance lets you create a specialized version of an existing class. Inheritance lets the new class reuse the methods and attributes of another class. ..."

-- Ken

use strict;
use warnings;

package Pod::PseudoPod::HTML::Book;

use base 'Pod::PseudoPod::HTML';

# ... your code goes here ...

1;
[download]

package Cow { use Moo; has name => (is => 'lazy', default => sub { 'Mooington' }) } say Cow->new->name

What should I read to learn building modules over existing ones?

A good idea is to assume you're not the first to have this question (whatever it is), and to search for the answer

How to install CPAN modules into ActivePerl, A Guide to Installing Modules, ... Yes, even you can use CPAN, A Guide to Installing Modules, Top 11 (GOOD) reasons not to use someone else's Modules, Top Seven (Bad) Reasons Not To Use Modules

perlnewmod, perlmodlib, ...

Tutorials: Perl documentation documentation, Searching Perl Documentation, How to RTFM