Most jugglers consider rings easier to juggle than clubs, yet they look much more appealing in the air than balls, so they're a great prop for performing. They're very sensitive to even gentle breezes however, so they're not usually great props for outdoor use. They're fun to pass, they offer unique possibilities for tricks, and they're a good prop for numbers juggling. If you can juggle 3 balls, learning 3 rings will come easily.
Most jugglers use flat, inexpensive plastic rings. There seems to be much less variation in the quality of these rings than there is in balls and clubs. They typically cost around $5 to $7 each, and one brand seems to be about as good as another. Since Serious Juggling carries many brands and styles, usually with the same prices you'd pay buying from the manufacturer, that's a good place to shop. Renegade makes some hollow plastic rings that are easier on your hands, but also more expensive.
Get comfortable throwing and catching one ring. When you throw a ring, bring it up high, up to shoulder height, before you release it. Give it a small snap with your wrist, like a throwing a Frisbee, but vertically. The spin stabilizes the ring in flight. Unlike juggling balls and clubs, when juggling rings you should reach up to catch the rings higher, near your shoulders. Jugglers usually throw higher with rings than with balls or clubs.
Once you're making good throws and consistent catches with one ring, move on to exchanging two rings, then move on to the cascade. To hold two rings in one hand, grip one between your middle, ring and little fingers and your palm.
If you're determined to juggle rings outdoors, try this: Tape pairs of rings together. A few wraps of electrical tape at four points around the pair will hold them together nicely. The doubled weight makes them much less sensitive to wind, but it also makes a more substantial impact on your hands. This is a great use for broken rings. Just pair up broken rings with their breaks 180 degrees apart and tape over the breaks. Tape groups of 3 rings together and you'll be ready for some real gusts, and a workout keeping them up there.