Oh Gazucha; Hi !
Let me get my feet wet on this one... see if I can give direction to your perspective on "open source", ubuntu in particular.
The heart of this "movement" is the kernel, upon which everything else is applied onto. It had it's birth in the early 60's and since that time thousands of programmers in each generation have poured over this code, ever evolving this code to meet the desired applications. Anyone is allowed and expected to modify and/or enhance this code base to meet their needs and a number of systems have developed to meet the need of integration/enhancements for this code. -> one of which is the package management "system" and it is a system...fully integrated within any distribution installation.
Package management as a system is wonderful...there is at least 35 thousand "applications" made available, that thousands of people have done the work to make them available and tested to insure full compatibility with your chosen operating system and distribution. All available with the ease of -in the GUI, a click of a button, in terminal, "sudo apt-get install- and done !OK, so you need an application outside of the mainstream, some brilliant programmer has done the work, but his work has not to this time made it through the process to be accepted into the standard repositories ---The question now is how much work do you have to do to get his wonderful code to run on your particular machine ? It is indeed a rarity than one MUST compile from source - this is open source and that method can always be employed - but, what options has that programmer, and those supporting that program, made available to others to "install" this beautiful bit of coding ? Most often the program/application is available in the form of a "tar ball" or some other form of compression. In this instance some one has written the directions down for you ..the "readme file", after uncompression has been done.Or, maybe this brilliant programmer has gone 3 steps farther and made his work available through the package management system as his own Personal Package Archive ? Again it is but a matter of a few button clicks ...and done. The point here is that if one steps out from underneath the umbrella of the accepted software repositories, you have the work to do to attain your particular goal.... but it can be done... when all else fails, and it is that important to you.... write your own code for the benefit of all --- open source !
Comprehension and understanding this "operating system"; in it's complexity no one knows everything, but a lot can be known about somethings. Many people with great knowledge about a particular "something" make the contribution to the whole that is the operating system you have before you. In it's simplest terms -> the kernel gets loaded - the heart of the system, all else is appended in a modular fashion to this kernel that interacts and controls everything. Say a word processor, you interact with the word processor, the application interacts with the kernel to insure what you desire of the application gets done. What you ask is the means of your interaction with this kernel ? Why, the Command Line Interface ! And once more, no one knows all the commands available to interact with the kernel -literally thousands - systems are inplace to help you in the interaction ...most notable is the manual ---->man <command_name>. and the tools available within the manual system.
As said before, generations of coders to make the system you have before you... a constantly evolving system.... evolving, what was pertinent at some point in the past, may no longer be pertinent... things change and one has to keep up with how to interact with any particular.
You are correct in that one has to have a foundation to base comprehension on. The great thing about this movement is documentation is available. One has but to search and read...but read with discretion and discernment ...what does it apply to and why? ...what has changed in the operating system since the documentation was written ??? Many Many things change ...it is an evolving system. What was "then" might not even exist "now".
Millions of people have this operating system as their system of choice, there must be a solid reason for such popularity .... bottom line ...it works ! But to get beyond the point and click stage, one has to work too !
Just my opinion, open to debate