DHDR starts out just like a regular double hammock, except that the chest pass is bunched rather than spread across the chest. Genuine sling rings are then used to secure the tails coming over the shoulders via the bunched chest pass. The carry is thus secured after the two hammock passes but without the final reinforcement passes of the typical DH.
The size rings you use (usually medium or large) depends on the thickness of the wrap you are using - thick wraps need larger rings.
Here is a video to help you get started: https://www.youtube.com/watch?v=YYBo_45npIY&list=PLACEE5D957FF01294&index=23
Don't have rings? Our lending libraries have rings you can try at meetings!