Connecting a Rails Backend to a React Frontend
This article is a big picture look at how you can go about connecting a backend framework like Ruby on Rails to a frontend framework like React or Angular. I created this diagram to help make sense of how the process works.
This Harry Lavine article does a great job of walking you through the specifics.
I also recommend this youtube series by zayne for getting some exposure to one implementation of a Ruby on Rails backend working with a React front end.