I will focus on the basic knowledge about Linux.
linux is an open source operating system that can be used free of charge. Also, unlike OS such as windows and mac, it is lightweight because it has only the minimum functions, and the contents of the OS itself can be rewritten. Against this background, Linux occupies a large share not only in the PC field but also in the server field. That famous "android" also seems to be an OS made based on Linux. Great.
Unix Unix is the oldest operating system in existence and is still used in many situations like linux. If you know Linux, you may have heard of Unix once. That should be the case, and Linux is a Unix-like OS that is made with reference to Unix so that anyone can use it for free. It seems that "ios" is made based on Unix.
The "GUI (Graphical User Interface)" is a style in which a window is displayed and operated with a mouse, as we are familiar with in Windows and OS X. "CUI (Character User Interface)" is a style in which a command (command) is input to the GUI with the keyboard and the result is received in characters. * CUI is sometimes called "CLI (Command Line Interface)". Linux can be operated with either GUI or CUI.
** Articles about CUI **
Below are two articles that summarize commands, etc., centered on the CUI.
・ Introduction to Linux commands https://26gram.com/linux-command ・ Linux shortcut summary https://eng-entrance.com/linux_shortcut
I think that the contents including the above two articles can cover the basic knowledge and operation to some extent.