Sketch of a system for controlling home appliances with Arduino and WiFi via smartphone

I found a lot of specific solutions and ideas.
I did not find a general sketch of a system for controlling
home appliances with arduino and wifi via e.g. a smartphone.
Can someone sketch such a data flow diagram
From/to the controlled and controlling devices?

From a bird's eye view there is little concrete
and from the 23 pages of the Sensors article it is difficult to pick out
some factual information...
And what I would like to know about:
- how to transmit the result of the voltage measured by the arduino to the local LAN server - "private cloud"?
- how to tell the arduino to switch on one of the outputs when the local server finds such a command in the todo list?
- how is the communication and identification of each other - server and devices with arduino on board - secured?
It is not about specific programming language instructions, but about communication and security in such a network.

khoam wrote:

It is of course possible to write an elaboration of a dozen pages exhausting the subject,

.
I have just tried to explain that this is not what I mean...It would be very helpful:
Arduino -> Server:
How to upload 12.0? Is the 8266 'transparent? Is there an Arduino - 8266 protocol? How to 'push' this to the server?
Analogously in the other direction... All in all, a few sentences or lines with commonly known symbols (for short:) )
In the meantime, I'm searching on the electrode and all over the web....

I have a couple of Atmega168's and so narrowly looking at the Arduino....
Does the 8266 include the above or is it just a buffer for wifi?
Thank you for another link.