Power Rings are the main source of powers for the Green Lantern Corps, the Sinestro Corps, and (possibly) various other groups.
Green Power Ring (Main)Edit
The Main Power Ring is the ring used by Jade. It is capable of flight (including extraterrestial), transforming the wearer's clothes into a black/green bodysuit, and pretty much anything the wearer wills it to do. It comes complete with an AI which can interface with the ship's computer (loaded with information on the ship and the various people Hal Jordan met on his travels) and all earth-based communications (including TV broadcasts, police radios and the internet). It is bound by the rules written in the Book of Oa. These rules have recently changed due to a war being staged elsewhere in the galaxy between the Green Lantern Corps and the Sinestro Corps.
The Power Rings of the Green Lantern Corps are powered by a mysterious 'green element' discovered by the Guardians of Oa. It is said to be the essence of Willpower, and there are legends of an entity known as The Ion that is traditionally associated with the green element.
The powers of all the rings are drawn from the Central Power Battery on Oa, which contains this green element. It is often said that the Green Lantern Rings are the 'most powerful weapons in the universe'. They seem only limited by the user's creativity and Willpower. There is a limit to how much Willpower a ring can take, but it is unclear what this limit is.
In the past, the Green Power Rings required their own Power Batteries (which look suspiciously like old-time Earth Lanterns, hence the name "Green Lantern"), and had to be recharged every 24 hours. There do exist more advanced Power Rings that do not require this procedure; it is unclear whether or not Jade's Power Ring is of this type or not. Green Lanterns can use their ring to create copies, ranging from a ring with nearly-identical powers to the original, or more limited abilities, typically used in emergencies, for deputizing other Green Lanterns on a temporary basis; whether or not Jade's ring can do this is unclear.
Green Power Ring (Lesser)Edit
The lesser power rings are currently produced by replicator aboard the Starship Jordan, and are bound to the will of the wearer. They have two main functions: communication with other ring bearers, and the ability to produce light-based illusions surrounding the wearer's body - usually clothes, but it can be used to subtely alter the wearer's appearance. The lesser Rings can also translate various languages for the wearer.
The rings may possibly be slaved to Jade's own, allowing her to keep tabs on the location of each Ring wearer.
Star Heart Power RingEdit
Crafted from a shard of the Star Heart itself, which fell to Earth, this Ring grants Alena Scott powers very similar to those of a Green Lantern, although they are magic-based, and do not draw upon the power of the green element. It is unclear exactly what the difference between Alena and Jade's powers are; something that seems easy for Jade to do, may not be so simple for Alena, and vice versa. Whether this is due to the differing power source, or simply because they are very different people is unknown.
Technically, Alena's ring has no real power of it's own, it serves a sort of magical foci, amplifying her Will and allowing her to more easily tap the power of the Star Heart within her body. Alena's psyche is actually the source of her various weak points; presumably, as she overcomes her fears, she will become much more powerful.
The Star Heart has a strong connection to 'the green', the energy field that unites all plant life in the universe. The benefits of this connection are similarly unknown, but the Star Heart Ring supposedly cannot directly affect wooden objects, and has much more limited powers when dealing with other plant life and matter.
Yellow Power RingEdit
So far only seen on Tekik, it appears to have similar powers to the main power ring, but without its own dedicated AI. These rings are recharged by spreading Fear, making them quite dangerous. Much like the traditional Green Lanterns, Sinestro Corps members typically use a Power Battery to recharge their rings from the Central Power Battery.
Tekik has internalized his Power Battery, allowing it to directly recharge itself without needing to contact the Central Power Battery; the reasons why it has done this are unclear.
The yellow element of Fear can erode willpower, and typically in a one-on-one confrontation, Sinestro Corps members can overpower a Green Lantern. The energy of a Yellow Power Ring can destroy green energy constructs on contact. Sufficient will can negate this effect, however, doing so quickly drains a Green Power Ring of it's energy.
It is likely for this reason that the Guardians gave their Green Lanterns permission to use lethal force against the Sinestro Corps, as a prolonged battle will most assuredly spell doom for a Green Lantern.
There are rumors of other elements besides the green and the yellow, and it is likely an element exists that weakens Sinestro Corps power rings. The entity of the yellow element is called Parallax; it was imprisoned by the Guardians for millenia, but it is now free to roam the universe once more.