I want to activate a sub by clicking the left mouse button but i cant make it work i tried
private sub test(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles MyBase.MouseDown

but it says it doesn't work because they dont have a compatable signature

Here's a sort of workaround

Private Sub MyMouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)
  ' Your "MouseDown"

End Sub

Private Sub Form2_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseDown
  ' Call MyMouseDown
  ' Trap left mouse button
  If e.Button = Windows.Forms.MouseButtons.Left Then
    MyMouseDown(sender, e)
  End If

End Sub

It traps form's mouse down event, checks that left button is pressed and calls a standard procedure with mouse down event's arguments.

HTH

Chris11246,
Did you notice?
This is your code:

private sub test(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles MyBase.MouseDown

and this is Tem's code

Private Sub Form2_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseDown
  ' Call MyMouseDown
  ' Trap left mouse button
  If e.Button = Windows.Forms.MouseButtons.Left Then
    MyMouseDown(sender, e)
  End If
End Sub

Function Signature : It means argument (parameters), and return datatype of function or sub.

To add an event handler:
1. Select a Control or Form
2. Open Properties Windws.
3. Select Event tab.
4. Double click on the name of event you want to handle.