in what folder i add js code with react code example

Example 1: how to import js via script in react

import { useEffect } from 'react';

const useScript = url => {
  useEffect(() => {
    const script = document.createElement('script');

    script.src = url;
    script.async = true;

    document.body.appendChild(script);

    return () => {
      document.body.removeChild(script);
    }
  }, [url]);
};

export default useScript;

Example 2: different ways to write react file paths

Writing a path to a react file/project file
import something from '/thatThing'; this is the current tree
import something from '../thatThing';
import something from '../../thatThing';

dipending on your level of files you should be able to find a way to map through your project files with this tips.