The rings pictured here are Walnut and Hickory. I haven't tried these out of soft wood such as pine, but I do not think they would work to well so stick to a hardwood.
These really are very simple, the hardest part is getting the sizes right. Once you have the process down you can crank them out quick.
Step 1: Gather some scrap wood.
You will also need a larger junk piece of wood attached to your lathe and turned with a taper to a dull point that will hold the ring by friction (jam-chuck). I am using some scrap pallet wood. A 2X2 would work fine for this. I actually think a softwood would work better for this.