As you know, Devuan is using a little bit different init system (sysvinit), than majority of linux distributions (systemd). It means, that you have a chance to follow system's startup and shutdown processes in detail. Moreover, sysvinit gives you a chance to adjust, modify and configure the way, how processes get started.
First process created in system has PID=1 and runs as a daemon. PID number 1 controls system's startup, shutdown and every changes happening with other proceses.
What is inittab
Let's see, how you Devuan system starts: Bootloader starts kernel, which spawns init, which parses inittab, which starts a service symlinks in the boot runlevel and then in the default operating runlevel.
Inittab is just a file, which describes and sets, which processes start in which runlevel. Let's see on a real example and explain, what means what.
To view an inittab, run a command:
$ cat /etc/inittab