Squealer uses language to keep Napoleon in power. His use of language helps to construct truth that is acceptable to the power structure. He uses language as a means to consolidate power. This conception of control extends to the use of language to explain both past and present in a manner that enhances the power of the status quo. In this light, truth is an element that can be malleable through language. His use of language is designed to enhance the control that the pigs have over the rest of the farm. There is always an answer, always an explanation, and these invariably substantiate the ruling party. It is in this light that Squealer uses language and its enhancing of social control.
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.