Animal Farm begins with the owner of Manor Farm, Mr.Jones.  He comes back to the farm drunk, yet again, and forgets to do many things for the animals such as shutting the popholes for the henhouses.  That very same night, Old Major calls all the animals in the farm into a meeting to explain a dream that he had.  His dream was about how all Man had vanished and all animals were free.  He continues with his speech by pointing out what cruelties that the animals have faced or will if they're still being ruled by Man.  Three days later, Old Major dies peacefully leaving his speech in the minds of many animals.  Suddenly one day Mr.Jones forget to feed the animals, so they begin to rebel and charge into the food stock.  Mr.Jones tries to stop the animals, but then he stops when the animals start charging at him in an angry uproar.  Two of the smartest pigs, Snowball and Napoleon, begin to take charge.
The Seven Commandments is created at the basics of Animalism and all animals should live by them.  They were created based on the ideas of Old Major's speech.  Although, because most of the animals cannot read, this creates a problem when they're changed without any notice.  Snowball is the only leader that actually ruled to help the animals, and does not abuse his power for his own good unlike Napoleon.  When Snowball is helping the farm restore order, Napoleon is secretly training his own secret police, the dogs, which later on in the story he uses to manipulate the other animals and eventually drive out Snowball. 
Throughout the whole story, Squealer brainwashes the other animals into believing that Napoleon is a great leader, Snowball has always been on Jones side and that some of the things that the pigs do is for their sake so Jones does not come back.  Some propagandas that Squealer uses against Snowball is that he destroyed the windmill (when it was really the weather, strong winds), vandilized the farm at night and that he wasn't really a hero during the Battle of Cowshed.