In Chapter One of 1984, Winston writes in his newly-purchased diary for the first time. This diary is used by Winston as a tool for self-expression because, under Party rule, Winston is not allowed to articulate his thoughts and feelings. Merely possessing a diary in Oceania is a punishable offense: Winston faces at least twenty-five years in a "forced-labour camp," or even the death sentence if his diary is found. Moreover, the contents of the diary constitute Thoughtcrime, an extremely serious offense in Oceania, which is again punishable by death or, at the very least, a visit to Room 101.
For Winston, however, the need to express himself is stronger than his fear of being detected. While his words on the page seem like a "stream of rubbish," they, in fact, represent a conscious effort to resist the Party and its indoctrination. Specifically, he needs an outlet for his discontent, as we see through his first entry when he critiques his evening at the cinema. As such, the diary should be viewed as the beginning of Winston's rebellion and as a necessary part of his awakening.