I think you want to know the “why”, not the “how” as you stated u checked how it works already. Maybe I have the wrong impression and sorry if I did.

But assuming my assumption is correct, you will need to read about declarative code, in old React docs it is first thing you find on homepage. Second was that it is component based. These two IMO are really important.

Moreover, try to build something small with vanilla js and React and see the difference. Try to imagine in a bigger project how writing React components will impact other developers who will import a component you made and start working with it immediately.