How do you exit the operating system on computers?
Basically, you shut the computer down. Procedure for that
depends on the specific operating system. Operating system is what
makes a computer do things. Even the thing the loads the main
operating system for a given computer is a small operating system
in itself. For example, the thing that loads Windows or Linux up is
called BIOS, and that stands for Basic Integrated Operating System.
Once you exit all the operating system(s) you may as well shut down
the machine (if it does not shut down by itself.)