Server

Enter to the server folder from a terminal and start the server

rails server 

Client

While the server running, create another terminal and enter to the client folder and start the React app

yarn start 

References

https://www.youtube.com/watch?v=kSlJH3hrV58&t=166s

https://www.youtube.com/watch?v=1eNrZFXH9X8&t=573s

https://web-crunch.com/posts/how-to-use-graphql-with-ruby-on-rails-part-2

https://graphql-ruby.org/guides#subscriptions-guides