Anyone who has been asked to go for a police check can apply for an Australian police check online. You can do so through various websites but it will have to be issued by the Australian Federal police if you are from Australia and assuming you are from there then you will also have to meet their requirements.
If you are under 16 then it would be difficult for you to get an AFP Police check as the minimum age for it is usually 16. Likewise, if you have hardly spent any time living in Australia then you may not be able to get an Australian Federal police check so you will have to first meet the requirements in order to qualify for it.
And if you have lived there for more than 12 months given that 12 month is the minimum that you should have lived in Australia in the past 10 years then you will be able to get it but you will have to pay a small fee to gain access to an Australian Police check. This is a seamless process once you have done it for the first time.
If you are doing it for the first time then you may want to refer to different websites for information on what an Australian national police check online entails and how to go about getting one for yourself. And the Australian Federal police check is usually valid for one year which means you may want to do it again in future should you require it as old reports would not be acceptable.