Rooting questions + How can i convert to stock to get ota updates ?

So i am super new to modifying android devices so i would like to know a few things.
What is a recovery / stock recovery ?
What is a rom ?
What is S-OFF, what can i do with it, and how do i achieve it ?

How can i revert everything so i can update it or where can i find the packages to update it ?

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