That's really the crux of it. The home automation software handles the management of the Z-Wave devices and provides a mechanism
for automating control of those devices when events occur. MQTT allows other software, such as
Blue Iris, a straightforward way to
send those events to the home automation software.
There are several good home automation packages, and the choice on which one to implement often comes down to the degree of
complexity and configuration the user wants. I use Home Assistant, Blue Iris, and MQTT and it all works well. I am
happy to provide details on my hardware and software, but I don't want to bore anybody (further), so, I will include a couple of screenshots,
that might make the process a little more tangible.
Blue Iris as an MQTT client pushes a message to the MQTT broker with a topic and payload - in this case, my
"driveway_right" camera. Note that the
text for the MQTT topic and payload is just something I made up, but it has to
be formatted with slashes as shown (that's not entirely accurate - you could just subscribe to something like "blue_iris" to receive
all events, but you would have no idea which camera or device sent the message.)
Camera Settings--> Trigger--> Immediate actions...--> Web request or MQTT:
View attachment 153901
And similar to the Homeseer 3 screenshot above, Home Assistant provides something called an "Automation" which has Triggers, Conditions, and Actions.
A "Trigger" can be an MQTT message:
View attachment 153902
and then an "Action" (turn on a Z-Wave switch in this case):
View attachment 153898
It can get complicated pretty quickly if you want, with various conditions, multiple areas, devices, and entities, but hopefully this helps.