VBA Brain Needed!

DominicB gave me this VBA code. I thought I'd be able to figure out how to adjust it for my worksheet. Apparently, I am not that bright. Can someone please help? I have two tables with ranges, B3 to I11, and B15 to I23. The first table is pulling from L3 to S11, and the second pulls from L15 to S23. How do I enter those parameters into this code? Thanks Much!

Sub test()
a = Selection(1).Row
For n = a To Selection.Count + a
For f = a To Selection.Count + a
If Cells(n, 1).Value = Cells(f, 3).Value Then
Cells(n, 1).Interior.ColorIndex = Cells(f, 3).Interior.ColorIndex
End If
Next f
Next n
End Sub

Please edit your post to add code tags, and amend the title to be descriptive of the problem.

Thanks.