Create a command by inheriting from BaseCommand
CommandInheritingBaseCommand\ZoomToLayer.vb
' Copyright 2010 ESRI
' 
' All rights reserved under the copyright laws of the United States
' and applicable international laws, treaties, and conventions.
' 
' You may freely redistribute and use this sample code, with or
' without modification, provided you include the original copyright
' notice and use restrictions.
' 
' See the use restrictions.
' 

Imports System.Runtime.InteropServices
Imports System.Drawing
Imports ESRI.ArcGIS.ADF.BaseClasses
Imports ESRI.ArcGIS.ADF.CATIDs
Imports ESRI.ArcGIS.Framework
Imports ESRI.ArcGIS.ArcMapUI

<ComClass(ZoomToLayer.ClassId, ZoomToLayer.InterfaceId, ZoomToLayer.EventsId), _
 ProgId("CommandInheritingBaseCommand.ZoomToLayer")> _
Public NotInheritable Class ZoomToLayer
    Inherits BaseCommand

#Region "COM GUIDs"
    ' These  GUIDs provide the COM identity for this class 
    ' and its COM interfaces. If you change them, existing 
    ' clients will no longer be able to access the class.
    Public Const ClassId As String = "92a9664b-e3e3-43b9-a758-a3157981868a"
    Public Const InterfaceId As String = "4d2eda59-1721-4575-bec1-43c9f0163959"
    Public Const EventsId As String = "cdfcbab2-2be5-4ee0-adf5-8cd069c9fd2b"
#End Region

#Region "COM Registration Function(s)"
    <ComRegisterFunction(), ComVisibleAttribute(False)> _
    Public Shared Sub RegisterFunction(ByVal registerType As Type)
        ' Required for ArcGIS Component Category Registrar support
        ArcGISCategoryRegistration(registerType)

        'Add any COM registration code after the ArcGISCategoryRegistration() call

    End Sub

    <ComUnregisterFunction(), ComVisibleAttribute(False)> _
    Public Shared Sub UnregisterFunction(ByVal registerType As Type)
        ' Required for ArcGIS Component Category Registrar support
        ArcGISCategoryUnregistration(registerType)

        'Add any COM unregistration code after the ArcGISCategoryUnregistration() call

    End Sub

#Region "ArcGIS Component Category Registrar generated code"
    Private Shared Sub ArcGISCategoryRegistration(ByVal registerType As Type)
        Dim regKey As String = String.Format("HKEY_CLASSES_ROOT\CLSID\{{{0}}}", registerType.GUID)
        MxCommands.Register(regKey)

    End Sub
    Private Shared Sub ArcGISCategoryUnregistration(ByVal registerType As Type)
        Dim regKey As String = String.Format("HKEY_CLASSES_ROOT\CLSID\{{{0}}}", registerType.GUID)
        MxCommands.Unregister(regKey)

    End Sub

#End Region
#End Region


    Private m_application As IApplication

    ' A creatable COM class must have a Public Sub New() 
    ' with no parameters, otherwise, the class will not be 
    ' registered in the COM registry and cannot be created 
    ' via CreateObject.
    Public Sub New()
        MyBase.New()

        ' TODO: Define values for the public properties
        MyBase.m_category = "Developer Samples"  'localizable text 
        MyBase.m_caption = "Zoom To Layer VBNet"   'localizable text 
        MyBase.m_message = "Zoom to the extent of the active layer in the TOC"   'localizable text 
        MyBase.m_toolTip = "Zoom To Layer VBNet" 'localizable text 
        MyBase.m_name = "DeveloperSamples_ZoomToLayerVBNet"  'unique id, non-localizable (e.g. "MyCategory_ArcMapCommand")

        Try
            'TODO: change bitmap name if necessary
            Dim bitmapResourceName As String = Me.GetType().Name + ".bmp"
            MyBase.m_bitmap = New Bitmap(Me.GetType(), bitmapResourceName)
        Catch ex As Exception
            System.Diagnostics.Trace.WriteLine(ex.Message, "Invalid Bitmap")
        End Try


    End Sub


    Public Overrides Sub OnCreate(ByVal hook As Object)
        If Not hook Is Nothing Then
            m_application = CType(hook, IApplication)

            'Disable if it is not ArcMap
            If TypeOf hook Is IMxApplication Then
                MyBase.m_enabled = True
            Else
                MyBase.m_enabled = False
            End If
        End If

        ' TODO:  Add other initialization code
    End Sub

    Public Overrides Sub OnClick()
        Dim mxDocument As IMxDocument = GetMxDocument(m_application)
        ZoomToLayerInTOC(mxDocument)
    End Sub

#Region "Zoom to Active Layer in TOC"
    ' ArcGIS Snippet Title: 
    ' Zoom to Active Layer in TOC
    '
    ' Add the following references to the project:
    ' ESRI.ArcGIS.ArcMapUI
    ' ESRI.ArcGIS.Carto
    ' ESRI.ArcGIS.Geometry
    ' 
    ' Intended ArcGIS Products for this snippet:
    ' ArcGIS Desktop
    '
    ' Required ArcGIS Extensions:
    ' (NONE)
    '
    ' Notes:
    ' This snippet is intended to be inserted at the base level of a Class.
    ' It is not intended to be nested within an existing Sub or Function.
    '
    ' Use the following XML documentation comments to use this snippet:
    ''' <summary>Zooms to the selected layer in the TOC associated with the active view.</summary>
    '''
    ''' <param name="mxDocument">An IMxDocument interface</param>
    ''' 
    ''' <remarks></remarks>
    Public Sub ZoomToLayerInTOC(ByVal mxDocument As ESRI.ArcGIS.ArcMapUI.IMxDocument)

      If mxDocument Is Nothing Then
          Return
      End If

      ' Get the map
      Dim activeView As ESRI.ArcGIS.Carto.IActiveView = mxDocument.ActiveView

      ' Get the TOC
      Dim contentsView As ESRI.ArcGIS.ArcMapUI.IContentsView = mxDocument.CurrentContentsView

      ' Get the selected layer
      Dim selectedItem As System.Object = contentsView.SelectedItem
      If Not (TypeOf selectedItem Is ESRI.ArcGIS.Carto.ILayer) Then
        Return
      End If

      Dim layer As ESRI.ArcGIS.Carto.ILayer = TryCast(selectedItem, ESRI.ArcGIS.Carto.ILayer) ' Dynamic Cast

      ' Zoom to the extent of the layer and refresh the map
      activeView.Extent = layer.AreaOfInterest
      activeView.Refresh()

    End Sub
#End Region

#Region "Get MxDocument from ArcMap"
    ' ArcGIS Snippet Title: 
    ' Get MxDocument from ArcMap
    '
    ' Add the following references to the project:
    ' ESRI.ArcGIS.ArcMapUI
    ' ESRI.ArcGIS.Framework
    ' ESRI.ArcGIS.System
    ' 
    ' Intended ArcGIS Products for this snippet:
    ' ArcGIS Desktop
    '
    ' Required ArcGIS Extensions:
    ' (NONE)
    '
    ' Notes:
    ' This snippet is intended to be inserted at the base level of a Class.
    ' It is not intended to be nested within an existing Sub or Function.
    '
    ' Use the following XML documentation comments to use this snippet:
    ''' <summary>Get MxDocument from ArcMap.</summary>
    '''
    ''' <param name="application">An IApplication interface that is the ArcMap application.</param>
    ''' 
    ''' <returns>An IMxDocument interface.</returns>
    ''' 
    ''' <remarks></remarks>
    Public Function GetMxDocument(ByVal application As ESRI.ArcGIS.Framework.IApplication) As ESRI.ArcGIS.ArcMapUI.IMxDocument

      If application Is Nothing Then
          Return Nothing
      End If

      Dim mxDocument As ESRI.ArcGIS.ArcMapUI.IMxDocument = (CType(application.Document, ESRI.ArcGIS.ArcMapUI.IMxDocument)) ' Explicit Cast

      Return mxDocument

    End Function
#End Region

End Class