Dim request As HttpWebRequest = HttpWebRequest.Create("http://www.google.com")
request.Proxy = New Net.WebProxy(ip:port)
request.Timeout = 5000 'set timeout
request.KeepAlive = False
Dim response As HttpWebResponse = request.GetResponse()
Dim sr As StreamReader = New StreamReader(response.GetResponseStream())
Dim pageSourceCode As String = sr.ReadToEnd()
If it is for an app that will be used by other people, look into supporting private proxies. You will need to give them the option to say "my proxies require username/password" by having a checkbox. They check the box, and it unlocks the Proxy Username and Proxy Password text boxes.
In your webrequest code, add a check to get the checkstate of the checkbox. If it is checked, then pass the credentials in the WebRequest.
Dim IP as string = "127.0.0.1"
Dim PORT as string = "8080"
Dim USERNAME as string = "TestUser"
Dim PASSWORD as string = "TestPass"
Dim proxy As New WebProxy(IP & ":" & PORT, True)
proxy.Credentials = New NetworkCredential(USERNAME, PASSWORD)
request.Proxy = proxy