In Part One, Chapter Five of 1984, Winston is lectured by his friend Syme on Newspeak, which is the official language of Oceania. Syme is an expert on Newspeak because he works in the Research department of the Ministry of Truth and is involved in the writing of the eleventh edition of the Newspeak dictionary.
According to Syme, the essence of Newspeak involves "cutting language down to the bone." In other words, it involves the elimination of words which the party deems unnecessary. We see this in Syme's handling of adjectives:
"A word contains its opposite in itself. Take 'good,' for instance. If you have a word like 'good,' what need is there for a word like 'bad'? 'Ungood' will do just as well."
He goes on to say that the purpose of cutting the language down is to "narrow the range of thought" and therefore eliminate the possibility of ever committing Thoughtcrime. It simply won't be possible to think something bad about the party because Newspeak will have removed all the words that make these feelings possible.
On a deeper level, the development of Newspeak is about enabling the party to control people's thoughts. They already control people's movements through the telescreens, but Newspeak will allow them to enter people's conscious and unconscious thoughts and manipulate them accordingly. If people are unable to articulate their dissatisfaction with the party, for example, they will (theoretically) be unable to feel it. And this, in Syme's words, will signal the party's total control over Oceania: "The Revolution will be complete when the language is perfect. Newspeak is Ingsoc and Ingsoc is Newspeak."