rocky you turn duvet cover inside out and grasp the two ends - put on two big pegs on them and shake the cover down. What I then do I throw the duvet over the bannister and button them that way. Sometimes I ask my neighbour but really don't like bothering them so gave it a go about 10 minutes. It does help my duvet is like a feather in itself and the duvet cover was light too.
I actually invested in some clothes pegs but I still got tied in knots. It was easier with my old duvet but this feather one seems to fight against me. If I ever win the lottery I am going to pay someone to do this chore for me.
I have tried that method. Worked ok the first time, but not every time, not sure why. Lot of a fuss IMO. They should have velcro fastenings on 3 sides and there'd be no need for strategies on how to get it on.
old geezer bought the 3 sided duvet some years back - although mine were zipped - zipper kept being caught in the cotton - were a nightmare - ended threw mine out.
Duvet covers sold in Holland have the fastenings on one side - much easier to put on for singles and doubles, but much the same as bottom fastenings for king size.