When using or administrating linux system you are usually confronted with a command line. There are no graphical aids such as mouse or windows to help you navigate through directories or edit files. Linux system from administration point of view consists of multiple configuration files so called config files. By editing or creating these files an administrator is changing the behaviour of various services available within the system. Another situation where you can encounter text files are log files.
This is a companion discussion topic for the original entry at https://linuxconfig.org/cat-command