Step 1 -> Click Button1 and display its properties.
Step 2 ->Set the HelpKeywordonHelpProvider1 property to "Your .CHM Topic". 
Step 3 -> Set the HelpNavigatoronHelpProvider1 property to "KeywordIndex".
Step 4 -> Compile and run your application

If you want to set using Code you can do like this

helpProvider1.HelpNamespace =

"C:/helpFile.chm";

HelpNavigator.KeywordIndex); //Set the Keyword

helpProvider1.SetHelpKeyword(Button1,

"Your .CHM Topic"); // Topic in help file.

helpProvider1.SetHelpNavigator(Button1,

Hope this will help all who wants to integrate F1 key press to open help file in windows application.

（希望这将帮助所有想要集成F1键以在windows应用程序中打开帮助文件的人。）

2. 这里主要用到HelpProvider类，它用于提供控件的弹出或联机帮助。

每个 HelpProvider 实例均维护一个对关联控件的引用的集合。若要使帮助文件与 HelpProvider 关联，请设置 HelpNamespace 属性。通过调用 SetHelpNavigator 方法并提供指定控件的 HelpNavigator 值来指定提供的帮助类型。通过调用 SetHelpKeyword 方法为帮助提供关键字或主题。若要打开特定主题的帮助，则应以 topicName.htm 的形式传入关键字。

若要使特定的帮助字符串与控件关联，请使用 SetHelpString 方法。如果用户在控件包含焦点时按下 F1 键，使用此方法与控件关联的字符串将显示在弹出窗口中。

如果尚未设置 HelpNamespace 属性，则必须使用 SetHelpString 方法提供帮助文本。如果同时设置了 HelpNamespace 和帮助字符串，则基于 HelpNamespace 的帮助信息优先。

HelpProvider 在 Help 类上调用方法来提供帮助功能。

HelpProvider控件可以挂起控件，显示帮助主题。
1.SetShowHelp()方法：设置指定控件是否显示帮助信息；
2.HelpNamespace()方法：设置帮助文件；
3.SetHelpKeyword()方法：为帮助文件设置关键字；
4.SetHelpNavigator()方法：设置显示帮助中的元素；
5.SetHelpString()方法：将帮助信息的文本字符串关联到控件上。

TestHelpProvider:

1. using System;
2. using System.Collections.Generic;
3. using System.ComponentModel;
4. using System.Data;
5. using System.Drawing;
6. using System.Text;
7. using System.Windows.Forms;
8. namespace TestHelpProvider
9. {
10. public partial class Form1 : Form
11. {
12. public Form1()
13. {
14. InitializeComponent();
15. }
16. private void Form1_Load(object sender, EventArgs e)
17. {
18. //将帮助信息的文本字符串关联到控件上，在相应控件上按下F1键时显示
19. helpProvider1.SetHelpString(textBox1, "Enter an age that is less than 65.");
20. helpProvider1.SetHelpString(textBox2, "Enter a 5 digit post code.");
21. }
22. }
23. }

3. 介绍了菜单项显示帮助文档：

The HelpProvider control is used to show how to link to specific keyword in a .chm help file.

private void mnuContentsHelp_Click(object sender, System.EventArgs e) 
{
        // Show the contents of the help file.
        Help.ShowHelp(this, hpAdvancedCHM.HelpNamespace);
    }

    private void mnuIndexHelp_Click(object sender, System.EventArgs e) 
{
        // Show index of the help file.
        Help.ShowHelpIndex(this, hpAdvancedCHM.HelpNamespace);
    }

    private void mnuSearchHelp_Click(object sender, System.EventArgs e) 
{
        // Show the search tab of the help file.
        Help.ShowHelp(this, hpAdvancedCHM.HelpNamespace, HelpNavigator.Find, "");
    }

4. 一个邮件介绍：

If you use F1HelpProvider control. When you press F1 on the active control It will shows a pop up with Text which you have set already. Follow the Steps Below: 

1. Select the F1HelpProvider control from ToolBox and Drag it to your Windows Form. 
2. Set the following code in the Page Load event of your Form. 

helpProvider1.SetHelpString(txtPinCode, "Please Enter Ur city pin Code."); 

In the above code txtPinCode is a TextBox. 
3. Then run your application by pressing F5. 
4. If you have focus on the Text Box Pin Code then press F1. It will shows a Message that you have set likely to be ToolTip.

5.一个最好的例子，看了就明白。

Donwload example project C# 2005 Express from:
http://www.help-info.de/download/CSharp_CHM.zip
The CHM file resides in the DEBUG folder and you have to do following before giving that a try:
to open the CHM file right-click the saved file, click Properties, and then click Unblock.

（他说需要对CHM文件做这样的操作，我试了，可以直接F1打开，你们要是有问题就按照步骤）。

下面是代码：

private void Form1_Load(object sender, EventArgs e)
        {
            // set F1 help topic for this form
            helpProvider1.HelpNamespace = Application.StartupPath + @"\" + sHTMLHelpFileName;
            helpProvider1.SetHelpNavigator(this, HelpNavigator.Topic);
            helpProvider1.SetHelpKeyword(this, @"/Garden/garden.htm");
            helpProvider1.SetHelpNavigator(this.btnStart, HelpNavigator.Topic);
            helpProvider1.SetHelpKeyword(this.btnStart, @"/Garden/flowers.htm");
            helpProvider1.SetHelpNavigator(this.btnExit, HelpNavigator.Topic);
            helpProvider1.SetHelpKeyword(this.btnExit, @"/Garden/tree.htm");
            helpProvider1.SetHelpNavigator(this.chkMain, HelpNavigator.Topic);
            helpProvider1.SetHelpKeyword(this.chkMain, @"/HTMLHelp_Examples/jump_to_anchor.htm#AnchorSample");
       }

Thanking you