Using Material Components - https://flutter.dev/docs/development/ui/widgets-intro#using-material-components - Flutter provides a number of widgets that help you build apps that follow Material Design. A Material app starts with the MaterialApp widget, which builds a number of useful widgets at the root of your app.

30_days_of_flutter_material_components.dart

import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Tutorial',
      home: TutorialHome(),
    ),
  );
}

class TutorialHome extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // Scaffold is a layout for the major Material Components.
    return Scaffold(
      appBar: AppBar(
        leading: IconButton(
          icon: Icon(Icons.menu),
          tooltip: 'Navigation menu',
          onPressed: null,
        ),
        title: Text('Example title'),
        actions: <Widget>[
          IconButton(
            icon: Icon(Icons.search),
            tooltip: 'Search',
            onPressed: null,
          ),
        ],
      ),
      // body is the majority of the screen.
      body: Center(
        child: Text('Hello, world!'),
      ),
      floatingActionButton: FloatingActionButton(
        tooltip: 'Add', // used by assistive technologies
        child: Icon(Icons.add),
        onPressed: null,
      ),
    );
  }
}