What is the difference between state and props in React?

Both props and state changes trigger a render update.

Props (short for properties) are a Component's configuration, its options if you may. They are received from above and immutable.

• So props can change but they should be immutable?
  
• When should you use props and when should you use state?
• If you have data that a React component needs, should it be passed through props or setup in the React component via getInitialState?