What are the importance of "beasts of england, battle of the cowshed, and the windmill?

Animalism is the ideology of animal equality that Old Major comes up with.  It is the ideology that the animals are supposed to follow after the Revolution.  "Beasts of England" is its anthem.  The Seven Commandments are the rules that are made up to summarize the teachings of animalism.  Sugarcandy Mountains are the place that Moses the Raven tells the animals that they will go after they die.  This is meant to make them not care so much about the Revolution.

The Battle of the Cowshed is fought by the animals against people who come to try to take Animal Farm back from the animals.