All you need to do to notch a bow is to cut a "V" shaped notch in the end of the shaft. I used 50 lb test monofilament for the bow string, not because it is a really excelent material just because it was readily available to me at the time. My not preference is probably a fishermans knot (Just because it is very simple & self locking). You tie one end and loop it around one of the notches. Then you tie another loop (same knot) and place it on the other notch.
You now have your simple quick bow <-_->
I will make a follow up instructable about arrows fairly soon