How does front-end (React) interact with back-end (Express)? - node.js

Question

I'm building a full stack app using MongoDB, Express, React, and Node. I've worked on projects with only front-end programming and I've worked on projects with only back-end programming. I used ejs to create views for Express, so I'm not sure how it would work with front-end views created through React. Also, I'm not sure how the CRUD operations would be used with React. I have very vague ideas.
What I know is that in package.json, the two are combined together when running the program. That's about it. Even with that I'm unsure. My question is: How does Express interact with React?
The kind of answers I'm looking for involve connections. Where and how does it click together? If React creates views, then how is Express connected to those views? Am I importing files? Am I writing ExpressJS inside React components? How does it display data onto the view from a database? Is app.get('/',...) enough? How does Express know which files to use when posting that data?

Answer 1

Simple way to connect react with express add proxy in json File.
{
"name": "create-react-app",
"version": "0.1.0",
"private": true,
"devDependencies": {
"husky": "^0.14.3",
"lint-staged": "^7.0.0",
"prettier": "^1.11.0",
"react-scripts": "^1.0.17"
},
"dependencies": {
"bootstrap": "^4.1.1",
"react": "^16.2.0",
"react-dom": "^16.2.0",
"react-router-dom": "^4.2.2",
"sanitize.css": "^5.0.0",
},
"scripts": {
"start": "react-scripts start",
"build": "react-scripts build",
"test": "react-scripts test --env=jsdom",
"eject": "react-scripts eject",
"precommit": "lint-staged"
},
"proxy": "http://localhost:3000/",
"lint-staged": {
"*.{js,json,css,md}": [
"prettier --write",
"git add"
]
}
}