Some clarification on Presentation, Set, Req et al

[NotTooTechy]

Probably a stupid thing, but I am trying to work out the correlation between "presentation" and "set req"

I understand the Presentation is a notification of sorts to the main system, but am unsure what I should be using and why for both "Presentation," and "set req" options.

So, here's what I have in the house, two systems, one for heating (240v baseboard), one for cooling (swamp cooler)
I have DHT-11 sensor in the lounge with NRF24L back to master.
I have a two-relay board at the mains box for the 240v baseboard supply with NRF24L back to master.
I have a three-relay board at the swamp for Low, High and Pump with NRF24L back to master.

What do I Present and what do I use for a "Set" command for the heating and/or cooling? There doesn't seem to be a Presentation type for "Relay" and no "Set" option for "On" and "Off."

Could someone please give me some examples of what and how to assign those combinations?

I am a Mechanical Engineer and Programmer used to seeing things in logical sequence and order, but this what-goes-with-what is a mystery to me.