Creating a thermostat

Dear all,
I have an rpi running with openhab 3.
The temperature reading are done though onewire.
Each room a sensor. Zigbee connection from deconz. These are working.

I want to create a kind of thermostat (the wanted temperature).
Sounds easy and I think it is. But there, I miss something.
Is this in the gui, in the metadata or in the sitemaps? It is not advised to combine text edit and the gui. Is this correct?
Which part of the documentation can you advise? Are there examples for the creation of this value (not the rules).
I see rules and actions, but first I have to create a value to compare.

Thanks for the advise

I strongly recommend reading through the Concepts section of the docs followed by the Getting Started Tutorial. That should give you a grasp of what each part of OH does and what it’s for, including that “values” or states are stored in Items.

What do you mean by “this”?

Again, it depends on what you mean by “combine”. It’s not advisable, for example, to have some Items in files and others defined through the UI. But it’s OK to have Items in files and Things defined through the UI.

See above for where to start. That should give you the base knowledge to know where to look next and to start trying things.