To do this move your mills have to be pretty advanced. If not you can break your neck and get paralyzed or die (serious).
First do a mill to get momentum, this is very important. Then catch yourself in a headglide/icey ice position so your in a hand glide position with your head on the floor (in this move who have to be really high, a little higher than 45 degrees and less than a headstand position).
Then quickly kick and do a mill on your head and catch yourself with both hands on your head while facing down.
Then quickly kick and let go with both hands and repeat the steps. You can't use your elbows while doing halos, your only supposed to be on your hands and head.
Remember this move is extremely dangerous if your mills are not advanced enough. Everything from your shoulders up and your arms down to your fingertips are endangered.