HA, fritzbox and comet dect


I’m using HA for ca 3 Month and now I want to create a heating automation, but I don’t really have understood what the best way is.

I have two Xiaomi Bluetooth sensors and 3 comet dect thermostats already added to HA and working.
Now I have to create an automation, is there a good first beginners tutorial for this?
Should I use automation or a blueprint?
How can I involve the xiaomi sensors?
How should I configure the fritzbox, that fritzbox and HA don’t make different things?

I would start simple and go more complex at the time. So I don’t want to use a config from github that I don’t understand.

TIA Micha