You have to understand where fantasy comes from and from who it comes from to understand the metaphors involved, along with knowing all world history and Biblical history helps — so buckle up and enjoy :).
Tolkien, who wrote Lord of a Rings, is usually credited for creating this fantasy world with the different traditional fantasy races, humans, elves, orcs, dwarfs and hobbits. Tolkien was very much a Catholic, meaning that his identity and his relationship with God combined with the entire old Jewish roots are what allowed him to create these great worlds of brilliant imagination. For example, the ring in LOTR represents sin, so when one is in a state of sin, or when one puts on the Ring, they (spiritually) are now very visible to the dark forces. Naturally, orcs are spawns of these dark forces, as was depicted in them spawning out of the earth in the LOTR series.
Biblically, in the time of Adam and some years after, humans were hundreds of years old; this is the time of the Oddessy and Illiad and great giant humans (cyclops, Nephilim) — all the legendary stories were true. Great warriors like Achilles danced and dominated their way around the battlefield. Then, at about the same time as The Flood, God had enough and said decided that humans will not live longer than around 120 years. God Speaks, and it happens.
Elves then are a metaphor for a race of better humans that existed in the past. Historically this was when God literally walked with Adam on the earth. This is why in LOTR, the elves are seen as never changing, never aging; they hearken back to a better time in history who also had special (magical) powers.
This is just skimming the surface of it, but you could google Catholic Analysis of LOTR. I'm sure oceans of ink have been spilled in this path we are going down, books even who can explain this much better and more accurately in all its details that I can. Enjoy and God bless.