Recently I wrote two articles that tried to explain Tolkien's mythology on Lord of the Rings in fairly plain terms. You can read them here and here.

Jaime writes:

Brad- thanks for your helpful, plain language articles. Just rewatched the first movie with a bunch of friends, and even those of us who read the Silmarillon, etc. couldn't remember them well enough to answer some background questions that your articles answered nicely. We still have some questions I thought you might know the answers to:
 

1) What's the deal with the 19 other rings? Who made them- it says in the movie  "they were all deceived' and we know Sauron could control them through the one ring, so did he make them and hand them out in disguise?
 

2) We know that the corrupted kings who bore  the 9 rings for men became ringwraiths. Were they numinor kings? And why was Isildur spared? And what happened to the elf and dwarf rings- were their bearers able to keep using the rings?
 

3) Nobody could remember- what's the deal with Aragorn being exiled? How long has it been since Gondor had a king, and why is Aragorn recognized as the heir but still in exile?
 

4) Is Elrond the elf King, or just a leader elf?
 

1) There 20 rings total (including the one Sauron made).  But Sauron only made 1 ring.  The other 19 were created by the elves. Of those 19 that Jaime refers to, all but 3 of them were "touched" by Sauron.  You see, at one time, Sauron was able to take the guise of a noble and wise person. Remember in The Fellowship of the Ring when Saruman at first came across as Gandalf's friend? Sauron was able to do this to the elves but much more so. The elves had no idea that Sauron was a bad guy at this point and Sauron taught them the craft of creating these rings. So the elves created these rings. The greatest of the elven Ring Makers was the lord of Eregion named Celembrimbor.  He created the 3 most powerful of the rings which had special powers. Elrond, Gladriel, and Gandalf wore those rings (you can see the rings on their fingers in the movie even though they aren't really mentioned much).

Eregion was a land that was just west of Moria and was destroyed in the last war with Sauron and the elves aren't there any more. That's why the entrance to Moria that the fellowship traveled through was there in the first place - an easy way for the elves to visit the dwarves who, at that time, got along okay.

What I find amazing about this plot is how applicable it is today. Think of middle earth magic like software. Sauron, taking the guise of a wise, trustworthy teacher, showed the elves how to create these rings (software). But in doing so, he knew where all the back doors were, all the ways he could hack into the rings.

Then in secret he went and forged one ring that would be able to harness all the power of all those rings as well as those who wore them. Once he did that, the elves got rid of all but the 3 rings which they simply took off.  But to make a ring of such power to control so many powerful rings as well as such powerful minds, Sauron had to invest much of his native essence into that ring. Magic, in middle earth, is spiritual energy. It doesn't just come from no where. And it's not re-generating (i.e. it's not like mana). Every time you use some you have to invest some of your life force so to speak into it. Eventually all magical things fade. The 3 rings, it should be pointed out, were actually created to postpone the fading of all magical things and did a good job at it.

Anyway, Sauron recovered all but the 3 elven rings and then distributed them.  7 to dwarves and 9 to men.  The 9 men who took them became kings in their time but eventually became mastered by Sauron and a slave to his ring and faded into being wraiths -- the Ring wraiths aka the Nazgul.

2) The ringwraiths were "dark" Numenorians.  Before the fall of Numenor, Numenor had established colonies of conquest in Middle Earth. In their time, some of these leaders became petty kings who came in contact with Sauron and were granted one of the rings.  Isildur wasn't "spared", he and his family never trusted Sauron and thus were never ensnared.

A little note on how powerful Numenor was - Sauron pissed off the Numenorians at their high point by contesting them for control of Middle Earth. Sauron, at the height of his power, with a massive army went to meet the Numenorian army. But the Numenorian army was so powerful that Sauron's army fled without a fight and Sauron was taken prisoner and taken back to the island of Numenor. Of course, Sauron has other forms of power than brute force and as was written elsewhere eventually corrupted the Numenorians from within.  But it does go to show how powerful Numenor was. Sauron had his ring with him at the time and his army and was still so outclassed by the Numenorians that his army cowered in the presence of the Numenorians. Kind of makes Gondor look pathetic eh?

Now, with regards to the dwarf rings - they were eventually all lost. The rings were cursed since they were ultimately controlled by the 1 ring. Dwarves couldn't be controlled by Sauron but he could encourage their darker natures to grow and the result was that each of the 7 dwarf kings became fantastically rich as the rings they worse ultimately led them to great riches which became the foundation of the 7 golden hordes of treasure. Unfortunately, dragons eventually came in and took those hordes and consumed most of the rings. The Hobbit actually deals with 1 of those hordes whose dragon, Smaug, probably consumed one of the 7 rings. The dwarven rings I believe are all lost by the end of the stories.

3) That is a bit sketchy I agree. So here's my take on it. Aragorn was born in the north and early in his life he fell in love with Arwen. But Elrond made clear to him, "My daughter will marry no other than the king of Arnor and Gondor and the opportunity for reunion will be a long while coming by the terms of men." And so Aragorn went out into exile into the world to became the world's greatest warrior biding his time for the opportunity to one day reclaim the kingship. He did so quietly and under many names for he knew that Sauron would return and that eventually the 1 ring would be found and only then would he be truly tested.

Gondor had been without a king for a long while, hundreds of years. My knowledge on that a part is sketchy. The last king of Gondor I believe died in a plague.

4) That's a bit sketchy too. Not all elves are the same. Elrond, like Gladriel, is of the Noldor. That is a type of elf race. He is also partly a Sindarian elf. Heck, there's some Maiar blood in him too but we'll try not to get too complicated. 

By the time of Lord of the Rings, there just aren't enough Noldor elves left to be using the term King anymore. He's the lord of Rivendell. The last high king of the Noldor was named Gil-Galad who died fighting Sauron.  The opening scene of Lord of the Rings should have showed two people being killed by Sauron and not just Isildur's father. The other person who Sauron killed in single combat was Gil-Galad, high king of the Noldor.

But that was the last alliance of men and elves and after that the Noldor slowly migrated back to the far west and their numbers dwindled to the point where the "realm" of Elrond is basically a large bed and breakfast type place called Rivendell.

Elrond, by the way, was born in Middle Earth and was going on 7,000 years old by the end of the story.