Introduction

First, you must install Xamarin for Android.
Let's Start
1. Go to File -> New -> Project.
2. Select Android Application -> Give it a Name.
Before starting, have a look at Solution Explorer. An Android Application contains Properties, References, Assets and Resources and so on. Properties contain AssemblyInfo (the same as you saw in the C# project). The References folder contains Assembly Files (DLL files). The Mono.Android DLL assembly contains the C# binding to the Android API.
The resources folder contains a Drawable folder (that contains icons and images for the application), Layout (provides a designer surface for the application). Resource.Designer.cs contains auto-generated code. As we will start from the basics, delete the main.axml layout and the Activity1.cs file from the project.
3. Right-click on Layout then select Add -> New Item.
4. Add an Android Layout (named Main.axml) then click on Add and select it.
5. Drop a Button control from the Toolbox.
Set the Button text as "Click Me!" and id as "@+id/btn_Hello".
Main.axml code:
  1. <?xml version="1.0" encoding="utf-8"?>
  2. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  3. android:orientation="vertical"
  4. android:layout_width="fill_parent"
  5. android:layout_height="fill_parent"
  6. android:minWidth="25px"
  7. android:minHeight="25px">
  8. <Button
  9. android:text="Click Me!"
  10. android:layout_width="fill_parent"
  11. android:layout_height="wrap_content"
  12. android:id="@+id/btn_Hello" />
  13. </LinearLayout>
6. Add a new item then select Activity then click on Add.
Activity1.cs Code:
  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4. using System.Text;
  6. using Android.App;
  7. using Android.Content;
  8. using Android.OS;
  9. using Android.Runtime;
  10. using Android.Views;
  11. using Android.Widget;
  13. namespace Hello_World_Application
  14. {
  15. //Set the Label = "Hello World Application" which is displayed on the Top of the Application(in Title)
  16. //Set MainLauncher = true makes this Activity as a Main Activity and Application starts from this Activity.
  17. //Set Icon using Icon = "@drawable/icon"
  18. [Activity(Label = "Hello World Application", MainLauncher = true, Icon = "@drawable/icon")]
  19. public class Activity1 : Activity
  20. {
  21. //Creating Instance of Button
  22. Button btn_Hello;
  23. protected override void OnCreate(Bundle bundle)
  24. {
  25. base.OnCreate(bundle);
  27. //SetContentView
  28. SetContentView(Resource.Layout.Main);
  29. //Get btn_Hello Button control from the Manin.axml Layout.
  30. btn_Hello = FindViewById<Button>(Resource.Id.btn_Hello);
  31. //Creating Click event of btn_Hello
  32. btn_Hello.Click += btn_Hello_Click;
  33. }
  34. //btn_Hello Click Event
  35. void btn_Hello_Click(object sender, EventArgs e)
  36. {
  37. //Display a Toast Message on Clicking the btn_Hello
  38. Toast.MakeText(this, "Hello World Application by Anoop", ToastLength.Short).Show();
  39. }
  40. }
  41. }
7. Build and run the application. Start an emulator image if not started. Select the Running devices and then click on OK.
Note: the Emulator takes a lot of time to start. Enable USB Debugging on your Android Device and run your application on the Device directly; that is much faster compared to debugging on an emulator.
Final preview:
I hope you like it. Thanks.