Multiple instances on different raspberry pi

I am a new member of your community.
I complete setup on a raspberry pi and an odroid XU4 and I have UI up and running on both. I need to connect both as I had it on Domoticz, so to control from a master instance (odroid XU4) the slave (raspberry Pi).
I found that users use a slave.py, I have it also BUT I do not know how to use it / in which folder to place it. Another question is if I need to run slave.py every time manual or there is a automatic way to be run.

Sorry for my lack of knowledge, I tried hard to find solution by myself but it was a failure till now.