I have gone through Laravel beginners tutorial, and now I can understand every topics listed in those tutorials and have created my own project, but as I saw in those, the tutors were able to understand what each file was meant for and had the capability to edit it and change it as per their needs.
So how do they learn so deeply and from which source?
I will try brief what is said at Laravel Official Documentation
In the root directory of every Laravel project you can find the following directories:
The app directory, as you might expect, contains the core code of your application. Models, controllers, services, middlewares are stored here.
The bootstrap folder contains a few files that bootstrap the framework and configure autoloading, as well as a cache folder that contains a few framework generated files for bootstrap performance optimization. Commonly you don't need touch this folder.
The config directory, as the name implies, contains all of your application's configuration files. You have to set your database connections, email drivers, sessions storage configuration (and much more), here.
The database folder contains your database migration and seeds. If you wish, you may also use this folder to hold an SQLite database. Migrations allows you define your database without writing any SQL code. It's very useful if you are interested at versioning your database structure. See more info here
The public directory contains the front controller and your assets (images, JavaScript, CSS, etc.).
The resources directory contains your views, raw assets (LESS, SASS, CoffeeScript), and localization files. By default, views uses the view engine named blade, but you could change this in the config folder.
The storage directory contains compiled Blade templates, file based sessions, file caches, and other files generated by the framework. This folder is segregated into app, framework, and logs directories. The app directory may be used to store any files utilized by your application. The framework directory is used to store framework generated files and caches. Finally, the logs directory contains your application's log files.
The tests directory contains your automated tests. An example PHPUnit is provided out of the box.
The vendor directory contains your Composer dependencies and the libraries needed for you application. Each library installed through composer will be stored here.
The app folder contains the core code of your application. There different directories inside this folder, each one has an specific purpose:
The app directory ships with a variety of additional directories such as Console, Http, and Providers. Think of the Console and Http directories as providing an API into the "core" of your application. The HTTP protocol and CLI are both mechanisms to interact with your application, but do not actually contain application logic. In other words, they are simply two ways of issuing commands to your application. The Console directory contains all of your Artisan commands, while the Http directory contains your controllers, middleware, and requests. The routes of your application are defined in this directory also.
The Events directory, as you might expect, houses event classes. Events may be used to alert other parts of your application that a given action has occurred, providing a great deal of flexibility and decoupling. Check this link for more info
The Exceptions directory contains your application's exception handler and is also a good place to stick any exceptions thrown by your application.
The Jobs directory, of course, houses the queueable jobs for your application. Jobs may be queued by your application or run synchronously within the current request lifecycle. There is more info here.
The Listeners directory contains the handler classes for your events. Handlers receive an event and perform logic in response to the event being fired. For example, a UserRegistered event might be handled by a SendWelcomeEmail listener.
The Policies directory contains the authorization policy classes for your application. Policies are used to determine if a user can perform a given action against a resource. More info here.