How to really develop a multithreading application ?

I'm trying to write a simple URL downloader.

But I want a real mutithreading, For example I have 100 website and I want to download them 20 by 20. threadcount = 20

I want to use threadpool, but I don't know how. I couldn't find any real solution in anywhere about this.

My save class is
Class savePage
    Public url, filename As String

    Public Sub save()
        Dim wc As New WebClient
        wc.DownloadFile(url, filename)
    End Sub

End Class

Now I want to save 100 URL multithreaded (threadpool).

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Imports System
Imports System.Threading

Public Class Example
    Public Shared Sub Main()
        ' Queue the task.
        ThreadPool.QueueUserWorkItem(AddressOf ThreadProc)
        Console.WriteLine("Main thread does some work, then sleeps.")
        ' If you comment out the Sleep, the main thread exits before
        ' the thread pool task runs.  The thread pool uses background
        ' threads, which do not keep the application running.  (This
        ' is a simple example of a race condition.)

        Console.WriteLine("Main thread exits.")
    End Sub

    ' This thread procedure performs the task.
    Shared Sub ThreadProc(stateInfo As Object)
        ' No state object was passed to QueueUserWorkItem, so
        ' stateInfo is null.
        Console.WriteLine("Hello from the thread pool.")
    End Sub
End Class


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Visual Basic.NET

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