Hey Teegan,
It's unusual you'd be given an essay to do this early in this year, given short answers and ACs are typically taught beforehand. Before you start, having a look at high-scoring VCAA essays would help with general structure and writing style/vocabulary.
You need modern (from the past 12-18 months) media/language examples to write essays, typically 2 examples per body paragraph- these are collected throughout the year (which is another reason why essays aren't usually taught this early in the year.) These examples include news articles concerning language use, such as a media figure using inappropriate language/terminology and being publicly criticized for it.
Other language examples include interactions you hear IRL or in media, such as a close friend calling you "idiot"- which is entirely appropriate, given you two have a close social distance, and in this context it expresses affection and mutual comfort, not hostility. (This is common in the Australian cultural context.) You may have to look around old threads and Google for some more examples.
For the essay question itself, here are some ideas-
Consider the language you use in different situations- slang and colloquialisms with friends (you can give examples of these, the 'rarer/newer' the better), or Standard Australian English at school or work. A reason you might do this is because your social purpose is different in both contexts (building rapport vs upholding a professional image.)
Another example is a media figure using language that is deemed acceptable in the immediate situational context, but criticized in a broader context when it is reported in the media. This broader context is synonymous with the current cultural context, as right now, there is a movement towards PC language and language sensitivity. (Google "tony abbott shit happens" for a closer look)
Finally, you may consider ethnolects and Aboriginal English, and how appropriate they are deemed in the contexts they are used, as well as their public perceptions.
good luck, pm if you need more help!