Perhaps there is no other text editor you need to work with. study specifically. However, if you learn to work with Vim, then a person gets amazing advantages over other people. Vim is usually already installed on most Linux systems and basic skills working with it are simply necessary for most developers.

Because this editor has its origins in the times when there was no Internet at all, the mouse had not yet been invented, and computers were terminals with a cathode ray tube and a keyboard that did not have arrow keys, then working with this editor looks akin to the dances of a shaman for the uninitiated.

One of the important advantages of this editor is the plugin system. It is thanks to this system that it is possible to transform Vim like an IDE, get syntax highlighting, auto-suggestions, file system navigation and much more.

There are many resources to help you learn how to use this editor, but I thought, if vim has so many plugins, is there a plugin for learning functions the editor himself? And it turned out that yes, there is!

Is is called vim-tutor-mode! In order to install it you need first to install vim-plag - it is an extention manager for vim. Then in a file ~/.vimrc you should add this line: "Plug 'fmoralesc/vim-tutor-mode'" to finalize plugin installation call: :PlugInstall

If the plug in installed successfully, you can start it with command :Tutor.

The tutorial covers the basic functionality of the editor, including working with files, searching and replacing, editing, running operating system commands, and more.

The passage took me several days in small sessions of about an hour a day. Passed on the phone in Termux, on the computer it should be even faster.

Found a useful article on how to set up your own mail server. This is important to me - without such hints, setting up the server takes about twenty-four hours and with the instructions this can be completed in just a day. If not for some minor mistakes in the article, it could have been done even faster. After some time, the antivirus that I have installed according this article was uninstalled - this thing eats away almost a quarter of the RAM, which is slightly critical to me.

On the same site you can find of how to configure Apache, PHP and MySQL. I can not say that this information is very necessary - you can install them without such instruction, but with instruction it is easier.

The OpenVPN can be configured here according to this instruction. In my opinion, OpenVPN should be configured by every self-respecting specialist.

What useful links and instructions do you have?

Sometimes when when you develop, for example, an online shop you need the credit card number that passes the credit card validation test.

There are many sites that could give you a bunch of random cards e.g. this one.

But much simpler to remember couple of them so you do not need to copy paste anything fromt third party resources.

There are two numbers that can be used in this situations which can be easily remembered:

4111 1111 1111 1111

and 

4242 4242 4242 4242 

I did know about the first one but I did not know about the second one which is also quite easy to remember.