init command traditionally boots a Linux system to a specific system state, commonly referred to as its runlevel.
Runlevels determine which of the many available system services are started, as well as in which order they start. A special runlevel is used to stop the system, and a special runlevel is used for system maintenance. As you will see, there are other runlevels for special purposes.
You traditionally use runlevels to manage the system services running on a Linux computer. All these special files and scripts are set up during installation, but you can change and control them manually.