With help of an object of the type Graphics, it is very easy to make screen capture. Add the next method  to your form:

Public Function CaptureScreen() As Bitmap

  Dim objBitmap As New Bitmap(SystemInformation.VirtualScreen.Width, _
                              SystemInformation.VirtualScreen.Height)

  Using objGraphics As Graphics = Graphics.FromImage(objBitmap)
    objGraphics.CopyFromScreen(0, 0, 0, 0, objBitmap.Size)
  End Using

  Return objBitmap

End Function

Now you can call this function as follows:

PictureBox1.Image = CaptureScreen()

Happy coding!