The applications for .au domain names opens on March 24th 2022, and will be allocated depending on how long you have owned your domain name for - the longevity gives you a "Priority" and this priority is used to determine who will be granted ownership of the .au domain if multiple applications are received. You can check the priority of your domain names using this tool https://www.auda.org.au/tools/priority-status-tool
If anyone else has a version of your domain name ending in .au, then the priority allocation will be enforced. For example, I own webcoast.com.au and webcoast.net.au but I don't own webcoast.asn.au or webcoast.id.au. Maybe nobody does, but if someone does own one of those other ones and they also want to own the webcoast.au domain, then both me and them need to apply for it, and the priority allocation will determine who is allowed to own it.
If nobody else has a .au version of your domain name and you wish to apply for it, then there is no contention and you are granted immediate ownership.
Note that the application for the .au domain is just that, an application. The application fee (at this stage, $40+gst for one year) is payable regardless of whether your application is successful or not. If it is successful then you will be granted ownership of the .au domain and it will require renewing after one year. If other entities own the other versions of your domain name then they have 6 months to also make an application for the domian name, if they don't and yours is the only application then it becomes yours, if they do apply then the priority allocation is used to determine ownership.
If you don't want the .au version of your domain name eg [yourdomain].au then skip the rest of this section.
Note that I if you wish to secure your .au domain name, you need to use the same provider as who your existing domain names are registered with. If your domain names are registered with WebCoast I will be in contact in early March. If you have registered your domain names yourself then it is up to you to apply for the .au through your current provider, should you wish to.
Here are some info-graphics about the process which might make things clearer:
At this stage you might like to know the priority status of your existing domain names, you can check that here https://www.auda.org.au/tools/priority-status-tool