Capture The URL Of Open Internet Explorer Window?

I need help to capture the Url of my open internet explorer window.... I need it to go into the URL variable that i have created. Can i do this if so how? Whatever you come up with can you explain it for me as ive only just started and want to understand it.Here is a copy of my code so far:

Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim Webbrowser1 As Object
Dim URL As String

[code].....