Middle Earth maps/geography

[Inziladun]

That's Beleriand, which in the First Age was the northwest corner of ME. If you look at the extreme right of the map you'll see Ered Luin, the Blue Mountains that lie north and south of the Grey Havens in the LoTR maps. Beleriand was sunk under the Sea by a cataclysmic event you'll read about in the book.
One word on the Silmarillion: it is a bit hard to follow the first time you read it, so you might want to take your time. And then read it again to really understand it. That's what I did.