Orwell may have subtitled his novel "A Fairy Tale," but we're thinking it's more like a fable.
Let's get some terms straight. An allegory is basically an extended metaphor—a picture, poem, or story in which everything stands for something else, like how The Lion, The Witch, and the Wardrobe is an allegory about Christianity, or Twilight can be read as an allegory for Mormon marriage. (True fact. Google it.)
A fable, meanwhile, is just a short animal allegory with a clear moral. Remember the story about the tortoise and the hare? The grasshopper who sang all summer? The wolf in sheep's clothing? The goose and the golden egg? (If not, you can brush up here.) In all those stories, the animals stand in for people or behaviors: the slow and steady tortoise who laps the ADD hare; the lazy grasshoppers who don't store food for the winter; and greedy men who kill the goose to get all the eggs at once without realizing that you kind of need the goose alive to get the eggs. (These fables, BTW, go way back to Aesop, a Greek slave who wrote these bad boys down during his life between 620-560 B.C.E.)
Orwell's novel is a traditional animal fable, but it's also a more complex allegory for the events leading up to and following the Russian Revolution. Like Aesop's fables, Orwell's story is full of personified animals. It's simply told and has a few clear morals: power corrupts, utopian visions are doomed, don't beat the horse. This simplicity makes Animal Farm easy: it has a point to make, and it makes it clearly and concisely. Sure, there are points to debate—like why Napoleon is able to take over so efficiently, and just why Benjamin doesn't seem to get that the pigs are going to betray Boxer until he actually sees the van.
But, in general, it's easy and, even without all the details of Russian history, everyone can get it. That's the whole point of an allegory. No wonder you're required to read it.