I can give you only one view -- that of an individual who uses Perl for many tasks: system admin (*nix and Win); inventory management s/w, local (specialized) search engines, online catalogue and ordering systems... the last three for clients who came to me originally to have me build'em websites. So numerous prejudices will show.

To answer your initial inquiry "why one should prefer Perl...?" -- Because it will do the job, with minimum pain and stain; allow you to create rigorously tested programs; offer literally thousands of non-core modules for special purposes; and situate you, as YM noted above, in a community where mutual aid is a part of the culture.

But let me not omit a fact relevant to programming in any language: you gotta' learn it. There is no substitute unless you wish to do no more than cargo-cult code (often questionable) from 'some site on the internet.' Your choice of books -- esp. "Learning Perl" is good for someone new to the language AND to programming (you don't say whether you've programmed in any other language, before).

And here's another first things first :-). If you really mean an "ap" in the sense that originated with smart phones, tablets, etc. you'll find some threads here (hint: Super Search) that may be illuminating but you should probably consider other languages such as :-( java for instance, I acknowledge with regret) but if you mean an "ap" in the sense of a dynamic web function (ordering, searching, etc), then CGI and PSGI will be at the roots of what you need to know. The Tutorials section here includes excellent resources for learning Perl/CGI.

If you're really most interested in "web" projects, you're likely to need to know how servers (APACHE etc) work; have a pretty good notion of the protocols that underlie the web; have a thorough grounding with HTML (4 and 5) and CSS (at least thru 2). Most of those are topics you can absorb to a functional level in a very short time -- perhaps as little as a week or a month or two (since html is so 'English-like' and CSS originated as an alterative to some html tags the deal with appearances). But beware some 'tutorials' which espouse merely-faddish separation of 'substance' and 'presentation' and most of the hoohah advocating the 'semantic web.'

The list ("in steps") for which you ask and which go beyond the points above are not readily served up on a platter because we don't know to what extent you've mastered the skills you're going to need nor the precise goals you have in mind (for example, see preceding para). But in most cases, I suspect the next step is to start with small challenges -- write a script to find all the mp3s on you system or a script to consolidate .jpgs in a single directory or a script to say 'hello world' -- first in a terminal (command prompt window) and then in a browser....

At which point, you may be back with more particular questions. We hope so. PM exists to help you learn when you get stuck on a problem you've tackled.