[Belegorn]

The Sil, is an early history of the Elves, from when the Powers entered Ea and began to contruct it to when Eru created the Elves who're known as the Firstborn. Basically it revolves around the deeds of the Noldor who are a strain of the Elves who're the most skilled with their hands, as one can see with the most exemplary of their kind, in Fëanor. It has to do with them and their fight with Melkor who stole the Silmarils, although many of the Noldor did not come to Beleriand, which was drowned after the First Age, to get back the Silmarils. They wanted realms of their own to rule over. One thing you should note is the Oath of Fëanor which sneaks up constantly on the Elves in their battles with Melkor. We also learn of the ancestors of the Númenóreans, who were the ancestors of people like Aragorn and some of the people in Gondor, like the Stewards House and a few other houses of Dunedain left in the South Kingdom. Now even though a lot of the story is about the Noldor and Melkor, there are stories about other Elves, the Sindar who did not go to the West, heroes from among the Edain, 3 marriages of the Edain and Elves which resulted in the Númenóreans and Elrond. We also learn of where the Dwarves came from, a creation of the Smith "God" Aule who was impatient of waiting for the First-Born.

The 2nd part of the Silmarillion is apparently written by Elendil himself, and it's about the Númenóreans and the 2nd Age of Middle Earth, the rise and fall of that people, and the eventual overthrow of the 2nd Dark Lord. Their rise is due to their deeds in the FA [As allies of the Eldar- Elves] and in the 2nd, and their fall is their falling out with the Elves and the Valar do to their longing for immortality played upon by Sauron.

There is a 3rd part which is a basically a summary of the Lord of the Rings. You learn about the creation of the Rings, why they were created and their role in the events of the War of the Ring. Basically the Lord of the Rings is about the One Ring and how it should be disposed of, whether used or destroyed and of course the best course is to destroy it which will not be easy. Its destruction will in the end finally bring about a new age ruled by Men as there are 2 kingdoms ruled by bearers of 2 of the Rings which will no longer be free from the cares of Middle-earth after the One is destroyed since all Rings are tied to the greater One Ring.