The Party wages a ceaseless campaign to control the minds of its citizens. People quickly learn to self-censor any unorthodox ideas so as not to be arrested and accused of "thought crimes."
The Party is also working on its Newspeak dictionaries, which are meant, as Winston learns, to reduce the English language to a minimum number of simple words. This helps greatly with mind control because it reduces the citizens' capacity to formulate unorthodox thoughts.
The Party also uses surveillance to control thought. People know they are being spied on all the time, and for that reason it is best not to think in an unsanctioned way and risk showing, through a facial expression or a muttered word, that one is out of alignment with the Party's ideology.
Memory holes are everywhere, so if citizens find writing that does not conform to Party rules, they can quickly send it down a hole to be burned in a furnace. This encourages people to "forget" what is no longer considered the official truth.
(The entire section contains 3 answers and 528 words.)