Difference between npm start and npm run start

I have checked both commands npm start and npm run start, both works perfectly. I used create-react-app. But to make configuration changes in the CSS module, I run npm eject but it throws an error.

But npm run eject worked? I’m confused on why npm eject didn’t work. Can I configure this?

Below is my package.json:

  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test --env=jsdom",
    "eject": "react-scripts eject"
  }