what does the maincomponent of a react app do code example

Example 1: create react component class

class MyComponent extends React.Component{
    constructor(props){
        super(props);
    };
    render(){
        return(
            <div>
              <h1>
              	My First React Component!
              </h1>
            </div>
        );
    }
};

Example 2: create-react-app class component

npx create-react-app my-app --scripts-version react-scripts@2.1.7