On Manor Farm, the animals get the idea from Old Major that they aren't being treated with respect by the farmer, so they revolt against Farmer Jones, and start a new farm run by animals.
With the animals as the new owners of the farm, they learn to read and write, and so they come up with the 7 commandments. With the pigs as leader, the farm runs smoothly. Until a slight disagreement between snowball and Napoleon over whether to build a windmill or not.
Eventually, snowball was chased off of the farm by Napoleon, the new leader of Animal Farm. As leader, Napoleon makes changes to how the farm runs. For example, he forms a committee of pigs, rather than holding meetings.
"Life is good on Manor Farm!
Napoleon starts blaming Snowball for everything bad happening around the farm, and accuses some of the animals for conspiring with him. Napoleon starts killing any animals that he thinks may be challenging his power.
"Ha ha, he dead!"
The animals start wishing that Farmer Jones was still the leader, because now Napoleon is starting to act like a tyrant and treat the animals worse than the farmer did. The prior commandments have also been re-written by Napoleon.
Dam, my life sucks.
The animals on the farm are no longer equal, and they are starting to notice that the pigs are starting to behave like humans. For example Napoleon is now an alcoholic, and he can stand upright. The animals can no longer tell the two apart.