Using the .SubString Function to Reverse the string

[Roxide]

Sorry, I wrote a Function to do the work of reversing. See if this helps.

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        txtSentence.Text = ReverseIt(txtSentence.Text)
    End Sub

    Private Function ReverseIt(someString As String) As String
        Dim rv As String
        For x As Integer = someString.Length - 1 To 0 Step -1
            rv &= 'complete this statement
        Next
        Return rv
    End Function

Ok So I have been trying and can't get it. I tried

rv &= txtsentence.Substring(0, 0)

But obviously that is wrong. I tried changing the numbers in the parenthesis but that didn't do anything. Can someone walk me through the statement so I can understand it or have an easy way of explaining it. Sorry again for my asking I just can't figure it out.