system
Given the following post, respond as if you're commenting on Reddit:
human
[LOTR] What do the different magic rings do?

I know there was a big war fought over that One Ring. But I heard Gandalf, that big grey-haired vet of the war, had a ring himself! What gives? What does his ring do? How many of these things are they; what do they do; where can I find one here on Middle-Earth?
gpt
At the time the story is set there are only three rings left that Sauron does not have in his possession. They belong to Elrond, Galadriel and Gandalf. These three rings are used for preservation. Rivendell and Lorien are kept from waning and deterioration by their effects. 

Celebrimbor was the elf who made them centuries before. There were 20 in total, and 16 of them were corrupted by Sauron in his attempts to control the different people of middle earth, and he had a direct hand in their creation. The three rings that the Elves (and Gandalf) still have were not corrupted as Sauron had no part in their creation, but were still susceptible to the control of the one ring. 

Sauron gave 9 rings to the kings of men and 7 to the dwarf lords. When he created the One Ring these 16 ring wearers fell under his control. The kings of men, over time, turned into the Nazgul. When Sauron did this the Elves immediately realised what was happening and took their rings off. 

The reason why they wear them during the time the books are set is because Sauron did not have the ruling ring, so they were safe to use.