It's quite simply achieved with sheep or pig netting as seen in the picture below. The piece of netting that I use for the pile is obviously a bigger circle than the one below which is actually used for something else which I may show you one day. This actual size would probably be all you would need for a small garden as it's surprising how much leaves compress when trodden.
So, what you need to do is to fill the ring with leaves and then get inside it and give the leaves a good treading down and when you have the ring half to three quarters full of compressed leaves work your way around the ring on the outside pulling it up as you go. Don't take it right off, just maybe lift it around a foot at a time and then pile in more leaves and tread them. You can go to at least twice the height of the netting although if you have a smaller ring you may need to judge for yourself what height you can go as I have only ever done this with the larger size ring which is forced to be more stable at height than a smaller one.
I find the good place to site the pile is under a tree as it helps to keep the pile moist and therefore encourage better decomposition. If you experience a dry summer it would benefit the pile if you kept it moist by applying water. Any old water will do just to keep the pile moist.