UPDATE This project has been moved into several separate repositories.
I encourage you to check out wordexpress.io for documentation. This is a still a thing!
First, you'll need WordExpress Server. WordExpress Server is a GraphQL server built using Apollo Server. This connects to your WordPress database and provides you with an HTTP endpoint that you can send GraphQL queries. WordExpress Server uses WordExpress Schema, which is a GraphQL schema that provides GraphQL types and queries for querying
Second, you'll need to take a look at a starter kit. I have created a kit for Vue and for React. Fair warning, I've spent much more time developing the Vue starter kit than the React one. The starter kits provide you with everything you'll need to get up and running on the front end.