Need help about listbox control

hello friends
Can someone please explain me the 5th line.

VB Code:

Private Sub cmdgrowth_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdgrowth.Click
        Dim pop As Double = 1125000
        Const yr As Integer = 2005
        Dim year As Integer
        Dim fmtstr As String = "{0,4}{1,10:N0}"
        lstGrowth.Items.Clear()
        lstgrowth.Items.Add(String.Format(fmtstr, " Year", " Population"))
        For year = yr To yr + 7
            lstgrowth.Items.Add(String.Format(fmtstr, year, pop))
            pop += 0.019 * pop
        Next
    End Sub

Thanks a lot guys

http://msdn2.microsoft.com/en-us/library/txafckwd.aspx