How to connect MVC with React JS

Question

I both understand Asp Net Core MVC and REACTJS

But how do I connect to the 2 with each other

How can I create a Input in Reactjs and let  asp net core read whats in it
and how can Reactjs read asp net core data from the database

I have tried to look up articles and youtube videos but they were either out of date
or it was all about either learning Reactjs or Asp Net Core

A small example would be great.

 

 

Thanks!