Lets say your calulator display is a textbox, and that the buttons will contain only the number you want to use when they are clicked.
Private Sub Digit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bttn1.Click, bttn2.Click, bttn3.Click, bttn4.Click, bttn5.Click, bttn6.Click, bttn7.Click, bttn8.Click, bttn9.Click, bttnZero.Click
if sender is bttn1 then
textbox1.appendText(bttn1.text)
elseif sender is bttn2 then
textbox1.appendText(bttn2.text)
elseif
'repeat this for every button
end if