This idea is just one of the fun activities you can find in my "How to Have Fun in the Great Outdoors--Without any Special Equipment."
Your ring must look like this:
You will also need the other part of the pop can "tab"--the part that covered the opening of the can.
Now, hold the ring horizontally in one hand and the tab vertically in the other hand. The ring has two slots. Insert the wide part of the tab into the slot of the ring that is farthest away from you. Now, pull back gently on the ring and release.
With a bit of practice you will get the ring spinning through the air. Have contests to see who can spin it the farthest.