The Directors/Producers will have specific ideas about the characters they are casting for. This process allows them to look at the available actors to see who
best fits the story line.
They will need to know what you look like on camera, and whether you are as good as you say you are. Looks are important, but if you can't act then you won't be believed by an audience.
Expect to be nervous. This is normal. Even the producers/directors will be a little apprehensive.
Channel 7 often audition many people at once, so there may be an audience of other actors and actresses all going for the same parts. You will be asked to say your name, age etc, before reciting a learnt piece of script.
After your learnt piece and dependant on the type of production you may be given paired or group improvisations to see how you work with and react to other actors. Direction may be given to see how you respond.
All auditions are filmed so that the directors can look back at the tapes to see how you look on screen. This makes it fair as it is often hard to remember everyone.
Make sure you've done your homework. Can you make the rehearsal/filming dates? If you can't then there will be no point in you auditioning. You'd be wasting yours and everyone else's time.
Your auditions will be filmed so make sure you know your lines. If you can't remember and deliver your lines at this all important stage, then it will be unlikely that you'll get a main part, as this is key to being an actor.