Hi Chloe, my name is Amy and I'm in my final year of school in Australia, our education system is quite different to the UK. I find that our schools are much more laid back than the UK, and Year 10 is generally not a stressful or even relatively important year*; but in Year 11 and Year 12 it does get more intense. For Year 10 I believe you have to study all the basic subjects like maths/English/science/etc with 3 additional subjects of your choosing (e.g. art, geography, history, drama) but for senior years it does become any combination of subjects and you can drop/pick up whatever you like. In these final two years of school (11 & 12), we have a system of units, which sounds confusing but it's simple: keep in mind you need to have 12 units for Year 11 and 10 units for Year 12, and each subject has a certain amount of units (almost all subjects have 2 except for the extension/extra classes which have 1) so you've got to pick a combination that adds up to the corresponding number for your year level (generally 5-6 subjects). And all the subjects we have are basically what you've got in the UK with some extras (so you can continue studying all the ones you picked for gsce's). This all sounds confusing I know, but they'll explain it to everyone at the end of Year 10 because all the others in your grade will probably be super confused too (I was confused at that time too!). Also, we don't have sets except for English and math. We generally have 3 sets for each (being below average, average, and above average).
You get 4 exams on each subject yearly, and your Year 12 performance is what makes up your atar (which is a final score out of 99.95 for some reason, which *only matters for university course acceptance* nothing else!!). Honestly, nothing until the senior years is taken as seriously here (unlike UK universities who take gsce's into account, our uni's only look at your senior results). Everything related to senior years and after school/university will be explained to you along with everyone else. Also you should know that our schools always have teachers and a guidance counsellor that help individuals with subject selections and career paths so you'll have someone to go to if you feel stuck. And you will definitely make friends, don't worry too much about that 🙂 I think Australian schools are pretty good, obviously no one likes school but we get a lot of opportunities and our teachers are nice and really laid back. Just do your best to get work in on time and work out how to improve with every exam you take, and you'll do really well!
*Also: I don't believe there's any big Year 10 exam? We have multiple exams every year including end of year ones, but your Year 10 exams won't go towards anything except your yearly report (which is also relatively insignificant). You might be thinking of Minimum Standards, which are exams you have to take in Year 10 to basically prove that you know the minimum standard knowledge for numeracy/reading/writing (not at all difficult tests and you don't even have to study).