Hello Boertjie,
That's a good question. I'm afraid I have no knowledge of Australian coins. What I say here ranges from guesses, up to a small bit of knowledge of how coins from around the world should read on the CTX.
Some of the learning/training steps could still be useful for you.
All of your coins should read on the FE 12 line of the CTX screen. That's the 12th little square down from the top of the CTX screen. That 12th line of course goes from the very left of the screen, all the way across to the right side of the screen. All of your coins, and jewelry, should show on or near that 12th line.
Now, where on that 12th line your coins would read, I don't know. Would some show near the left side of the screen on the FE 12 line? Some in the middle of the screen on the FE 12 line? Some near the right side of the screen on the FE 12 line?
I would assume that in Australia, the more valuable coins would read toward the right side of the screen, just like here in the states. In this case, CTX Training 1 should be very useful to help you learn how to identify good signals. CTX Training 1 does not read very much trash. Trash is confusing. So, CTX Training 1 is by far the easiest and least confusing training step. If many of your Australian coins read in the detection area of CTX Training 1, as they do here in the states, CTX Training 1 would be an excellent search program for you to start to learn how to identify a 'good' signal. It is very easy to use.
CTX Training 2, 2a, and 3, are geared more for US coins. From CTX Training 1, you may want to go to CTX Training 2, and then to CTX Training 4. Or, you may want to skip 2 and go straight to 4. CTX Training 4 is still a slightly closed search program and a little easier to use than a more open program. But, it should find any Australian coin.
Here on Finds Treasure Forum there is a chart, CTX 3030 US Coin TID Chart, that lists where US coins show up on the CTX 3030 screen. I would think that there is a similar chart for Australian coins also. Perhaps you can ask about this in a post and someone can help you find the proper chart for Australia.
Good luck,
Harry