Somebody help me out. I want to make this calculator to work but don't know the right commands for them.

Here is my code (Done is VB.net):
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

End Sub

Private Sub Label8_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)

End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
txt1.Text = "1"
End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
txt1.Text = "2"
End Sub

Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
txt1.Text = "3"
End Sub

Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
txt1.Text = "4"
End Sub

Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
txt1.Text = "5"
End Sub

Private Sub Button6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click
txt1.Text = "6"
End Sub

Private Sub Button7_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button7.Click
txt1.Text = "7"
End Sub

Private Sub Button8_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button8.Click
txt1.Text = "8"
End Sub

Private Sub Button9_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button9.Click
txt1.Text = "9"
End Sub

Private Sub Button10_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button10.Click
txt1.Text = "0"
End Sub

Private Sub btn17_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn17.Click
txt1.Text = "."
End Sub

Private Sub txt1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txt1.TextChanged

End Sub

My knowledge of VB.net is pretty bad.
What do I need to make this calculator to work.
I got it to place the number clicked in the text box but I can only put one number at a time.
My book doesn't really explain what code to use for adding or anything else like that. Need help.

Pls. don't do it for me just guide me in the right direction. I would like to learn how to do it properly.