Mr. Jones is described as the ineffective, exploitative, abusive owner of the farm. In his speech to the animals, Old Major explains how Mr. Jones mistreats and exploits them purely for his own financial gain. He reminds the hens, for instance, that most of their eggs have not hatched into chickens, but have instead "gone to market to bring in money for Mr. Jones."
Old Major also reminds Boxer that as soon as he loses his strength, Mr. Jones will "sell [him] to the knacker, who will cut [his] throat and boil [him] down for the foxhounds." Jones is thus presented as cruel and parasitical. He takes from the animals and gives almost nothing back. Mr. Jones values the animals only according to the financial profit they can generate.
Mr. Jones is thus described in much the same way as Karl Marx described capitalists. Indeed, Marx described capitalists as parasites who exploited the labor of the working classes for their own financial gain. Mr. Jones is thus important in Animal Farm because he represents and highlights the injustices of capitalism from a Marxist perspective.
Throughout the novella, Squealer is employed by Napoleon to spread lies and to distract the animals from awkward truths about the way the farm is being run by the pigs. Squealer is described as "a brilliant talker" who "could turn black into white." He convinces the animals that the pigs need all of the milk and apples because they "contain substances absolutely necessary for the well-being of a pig." He also convinces the animals that Napoleon should make all decisions on behalf of all animals because otherwise, the other animals "might make the wrong decisions," which in turn might lead to the return of Mr. Jones.
The reader can see all of these lies for what they are, but the animals are too naive to question the veracity of what Squealer tells them. Squealer is thus important in Animal Farm because he highlights how important it is to question the propaganda that all governments distribute to try and keep power.