Where do I place this code and what else do I need to do for it to work?

Function SumIfByColor(InRange As Range, _
WhatColorIndex As Integer, SumRange As Range, _
Optional OfText As Boolean = False) As Variant
'
' This function will return the SUM of the values of cells in
' SumRange where the corresponding cell in InRange has a background
' color (or font color, if OfText is true) equal to WhatColorIndex.
'
Dim OK As Boolean
Dim Ndx As Long

Application.Volatile True

If (InRange.Rows.Count < SumRange.Rows.Count) Or _
(InRange.Columns.Count < SumRange.Columns.Count) Then
SumIfByColor = CVErr(xlErrRef)
Exit Function
End If

For Ndx = 1 To InRange.Cells.Count
If OfText = True Then
OK = (InRange.Cells(Ndx).Font.ColorIndex = WhatColorIndex)
Else
OK = (InRange.Cells(Ndx).Interior.ColorIndex = WhatColorIndex)
End If
If OK And IsNumeric(SumRange.Cells(Ndx).Value) Then
SumIfByColor = SumIfByColor + SumRange.Cells(Ndx).Value
End If
Next Ndx

End Function
--
AOP