2 Components

1.MyComponent.js

//define component
class MyComponent extends React.Component {
  render() {
    return <Text>My component!</Text>;
  }
}
//export component
export default MyComponent;

2.Main.js

//import component
import MyComponent from './MyComponent';
class Main extends React.Component {
  render() {
    //use component
    return <MyComponent>;
  }
}

3.AppRegistry

AppRegistry.registerComponent('MyApp', () => Main);