define doublethink. and how does "doublethinking" works?

Doublethink

Newspeak word with two mutually contradictory meanings. The first is used to refer to an opponent, and can be defined as habitually contradicting plain facts. The second is used to refer to a Party member, and can be defined as a loyal willingness to believe contradictory statements when the Party demands it, which allows for continual alteration of the past.