1. Introduction

This tutorial aims to guide you through the process of using Flutter to build web and desktop applications. Flutter is an open-source UI toolkit developed by Google that allows us to create beautiful and highly interactive user interfaces for mobile, web, and desktop from a single codebase.

By the end of this tutorial, you'll learn how to:

• Set up your development environment for Flutter web and desktop.
• Compile existing Flutter code into a client experience for web and desktop platforms.
• Understand the fundamental concepts of Flutter and how to apply them to web and desktop development.

Prerequisites:

• Basic understanding of Dart language. If you're new to Dart, check out this introductory tutorial.
• Flutter SDK set up on your machine. Check out the Flutter installation guide.
• A text editor or IDE. We recommend Visual Studio Code or Android Studio.

2. Step-by-Step Guide

Before we start, please ensure that you have the latest versions of Flutter and Dart. You can check this by running flutter doctor in your terminal.

Enable web and desktop support in Flutter by running the following commands:

For web:

flutter channel beta
flutter upgrade
flutter config --enable-web

For desktop:

flutter channel dev
flutter upgrade
flutter config --enable-macos-desktop

Note: Replace macos with windows or linux if you're not using MacOS.

Now let's create a new project:

flutter create my_project
cd my_project

To run your project on the web, use flutter run -d chrome. For desktop, use flutter run -d macos, windows, or linux based on your OS.

3. Code Examples

Let's start with a basic Flutter app.

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(this.title),
      ),
      body: Center(
        child: Text(
          'Hello, Flutter for Web and Desktop!',
        ),
      ),
    );
  }
}

4. Summary

In this tutorial, we've covered how to set up Flutter for web and desktop development, compile existing Flutter code for these platforms, and create a simple Flutter application.

To continue learning, we suggest delving deeper into Flutter's rich widget system, exploring its package ecosystem, and experimenting with building more complex apps.

5. Practice Exercises

1. Create a Flutter application that displays a list of items. When an item is clicked, navigate to a new screen that shows the item's details.
2. Build a Flutter app with a form that takes user input and displays it on a new screen.
3. Develop a Flutter desktop application that interacts with the system's file system to read and write files.

Remember, practice is key in mastering Flutter or any programming language. Happy coding!