There is not an official
tutorial or FAQ specific to apmd authored by the OpenBSD Project.
The apmd daemon is one of the many daemons that may be started automatically at boot time by the /etc/rc system, with variables controlled by /etc/rc.conf and /etc/rc.conf.local. If you look in /etc/rc.conf, you will see:
apmd_flags=NO # for normal use: ""
Because the /etc/rc.conf file changes from release to release, the best practice is to put local settings in /etc/rc.conf.local. My laptop has this in /etc/rc.conf.local:
apmd_flags="-A" # auto management by default on this system
For more information, see FAQ 10.3 and rc.conf(8)