How to simulate mouse click?

This examples clicks where the mouse currently is when the feature is in the "onn" state:

Public Class Form1

    Private onn As Boolean = False

    Private Declare Sub mouse_event Lib "user32" (ByVal dwFlags As Integer, _
      ByVal dx As Integer, ByVal dy As Integer, ByVal cButtons As Integer, _
      ByVal dwExtraInfo As Integer)

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        Me.KeyPreview = True
        Button1.Text = "Off"
    End Sub

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        onn = Not onn
        Button1.Text = IIf(onn, "On", "Off")
    End Sub

    Private Sub Form1_KeyPress1(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles Me.KeyPress
        If onn Then
            Select Case e.KeyChar
                Case "Z", "z", "X", "x"
                    mouse_event(&H2, 0, 0, 0, 0)
                    mouse_event(&H4, 0, 0, 0, 0)

            End Select
        End If
    End Sub

    Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click
        Debug.Print("Button2")
    End Sub

    Private Sub Button3_Click(sender As Object, e As System.EventArgs) Handles Button3.Click
        Debug.Print("Button3")
    End Sub

End Class