ATAR stands for "Australian Tertiary Admission Rank". It's basically a score that represents how well you did in high school compared to everyone else in Australia. If you want to go to university in Australia, your ATAR will be really important. It's kind of like a number that tells universities how smart you are.
To figure out your ATAR, lots of things are taken into account: your grades, how well you did in different subjects, and how hard those subjects are. It's not just about getting good grades, but also about how well you do compared to everyone else.
It's important to remember that your ATAR isn't the be-all and end-all. It's just one thing that universities look at when deciding whether or not to let you in. There are other ways to get into university too, like doing a bridging course or getting some work experience.
So, in summary, your ATAR is kind of like a number that tells universities how well you did in high school compared to everyone else. It's important if you want to go to university, but there are other ways to get there too.