new wooden door step - fixing and finishing

[jkn]

Hi all
    I'm considering having a go at replacing the wooden door step to
our back door. The original is loose and rotting.

I'm sure some of this will be clearer when I remove the (metal) door
frame - how is such a step fixed? Vertical frame fixings?

Also, any suggestions for treating/finishing such an item, subject to
heavy use, to prevent future rot? I was wondering about treating it
wilth liberal amounts of Teak Oil or similar...

    Thanks
    Jon N