Event Handling

To handle the events you need to do two things:
1) Declare a handler method with the required signature

public void Application_SheetActivate(object sh) 
{ 
} 

2) Connect your handler method to the Excel object model that raises this event

this.Application.SheetActivate += 
    new Excel.AppEvents_SheetActivateEventHandler(Application_SheetActivate) 

Visual Studio displays a popup tooltip and will actually generate most of this line for you.
As soon as you type "+" a popup tooltip will be displayed
If you press Tab key twice Visual Studio generates the rest of the line and the event handler for you automatically

You can also use the Properties window to add event handlers
Double click the workbook class
Click on the lightning bolt icon to show events associated with this object

A lot of the events in the Excel object model are repeated on the Application, Workbook and Worksheet objects
For a complete list of all the events, please refer to Excel > Macros > Events

Events and Methods with the same name

There are several cases when an object has both an event and a method with the same name
To handle these events you must cast your object to the interface that contains the corresponding event definition

Here is an example of how to declare an event handler for the Workbook level NewSheet event

public void Event_WorkbookNewWorksheet(object sheet) 
{ 
} 

gApplicationExcel.ActiveWorkbook.NewSheet += 
   new Excel.WorkbookEvents_NewSheetEventHandler(Event_WorkbookNewWorksheet); 

However there are a few events which have ambiguous names.
In these situations you must cast the object to the corresponding interface first.
Application object must be cast to AppEvents_Event.
Workbook object must be cast to WorkbookEvents_Event.
Worksheet object must be cast to DocEvents_Event.
Chart object must be cast to ChartEvents_Event.
You can avoid these ambiguous interfaces in VB.Net if you use WithEvents and Handles rather than using the AddHandler.

Workbook_Activate

Activate is the name of both a method and an event.

public void Event_WorkbookActivate() 
{ 
} 

((Excel.WorkbookEvents_Event)gApplicationExcel.ActiveWorkbook).Activate += 
    new Excel.WorkbookEvents_ActivateEventHandler(Event_WorkbookActivate); 

Addhandler CType(gApplicationExcel.ActiveWorkbook, Excel.WorkbookEvents_Event).Activate 
Public Sub Event_ApplicationNewWorkbook(ByVal workbook As Excel.Workbook) 
End Sub 

If you want to fire this event manually you can use the following code:

objworkbook = gApplicationExcel.Workbooks("WbkName") 
CType(objworkbook, Excel._Workbook).Activate() 

Worksheet - ListObject

This list is slightly different to the VBA Events

You can create ListObjects dynamically

Microsoft.Office.Tools.Excel.ListObject AddListObject( 
   Microsoft.Office.Interop.Excel.Range range, 
   string name) 

Public Function AddListObject( _ 
   ByVal range As Microsoft.Office.Interop.Excel.Range, _ 
   ByVal name As String) As _ 
   Microsoft.Office.Tools.Excel.ListObject 

Excel.Worksheet vstosheet; 
Microsoft.Office.Tools.Excel.ListObject listobject; 
vstosheet = ActiveWorkbook.Sheets(2).GetVSTOObject 
listobject = vstosheet.Controls.AddListObject(Range("A1","B10"), 
                     new System.Guid(---).ToString()) 

Worksheet - NamedRange

This list is slightly different to the VBA Events

You can create NamedRanges dynamically.

Microsoft.Office.Tools.Excel.NamedRange AddNamedRange( 
   Microsoft.Office,Interop.Excel.Range range, 
   string name) 

Public Function AddNamedRange( _ 
   ByVal range As Microsoft.Office.Interop.Excel.Range. _ 
   ByVal named As String) As _ 
   Microsoft.Office.Tools.Excel.NamedRange 

Worksheet - XMLMappedRange

This list is slightly different to the VBA Events
These cannot be created dynamically at run-time

Worksheet - OLEObject