In React, the user interface is built using components. A component is an independent and reusable part of the UI. Components can be both functions and classes, but the modern trend is to use functional components.

Types of Components:

• Functional Components: These are JavaScript functions that return JSX elements.
• Class Components: These are ES6 classes that extend from React.Component.

Example of a Functional Component:

              {`import React from "react";
      
              function MyComponent() {
                return <h1>Hello, World!</h1>;
              }
      
              export default MyComponent;`}