Handling gestures - https://flutter.dev/docs/development/ui/widgets-intro#handling-gestures - Most applications include some form of user interaction with the system. The first step in building an interactive application is to detect input gestures.

30_days_of_flutter_handling_gestures.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(
      // body is the majority of the screen.
      body: MyButton(),
    );
  }
}

class MyButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () {
        print('MyButton was tapped!');
      },
      child: Center(
        child: Container(
          height: 36.0,
          width: 100.0,
          padding: const EdgeInsets.all(8.0),
          margin: const EdgeInsets.symmetric(horizontal: 8.0),
          decoration: BoxDecoration(
            borderRadius: BorderRadius.circular(5.0),
            color: Colors.lightGreen[500],
          ),
          child: Center(
            child: Text('Engage'),
          ),
        ),
      ),
    );
  }
}