Mr. Jones is drunk. Again. He owns Manor Farm, by the way. Also, the animals talk. Work with it.
"Old Major" is a sort of revered, older, wiser boar-pig-dude on the farm. He has a dream, and the others, acknowledging his age, wisdom, and all around general superiority, gather around (campfire-style) to listen.
The cast of characters is introduced. You’ve got Jessie, Bluebell, and Pincher (three dogs), Boxer and Clover (horses, male and female respectively), Muriel (a goat), Benjamin (an old and cynical donkey, good friends with Boxer), Mollie (a silly mare), Moses (a raven), chickens, hens, ducks, two turtledoves and a partridge in a pear tree.
Old Major suggests that they have an uprising against the lazy, resource-sucking humans and run the farm themselves. He introduces some rules for the animals regarding loyalty, alcohol, money, trade, and specifies that no animal may kill any other animal. Keep an eye on those rules – they tend to change as the story goes on.
They all sing "Beasts of England," a lovely tune eliciting warm and fuzzy feelings of togetherness.