In the book, Squealer uses language to help Napoleon stay in power. He constantly puts particular spins on events and conditions and he uses slogans and such to help control the other animals.
He pleads with the animals, for example, to think of how Napoleon is just watching out for them. Napoleon would hate it, he says, if they fell for Snowball's tricks. Here Squealer is trying to get the animals to identify with Napoleon and feel grateful to him.
He uses slogans like "tactics, comrades, tactics" to drum ideas into their heads rather than having them think about anything.
So, by spinning the things that happen, and giving the animals slogans instead of explanations, Squealer helps to keep them under control.