You first need to create your Django site and your react app inside it :

django-admin startproject django_react
cd django_react
npx create-react-app react-app

Now you need to build your react app to generate static files :

cd react-app
npm run build

You're ready to start your Django site :

cd ..
python manage.py runserver

Every time you change your react app code, you need to generate your new static files. Go inside your react app folder and remove your build folder.

npm run build

YOUTUBE video : https://www.youtube.com/watch?v=FhkqMHxchZ8