Heyo! This is a friend of GodlyBuddha who got in to EBSS.
First off, there's a Science Reasoning examination. It's easy, if you know the year 9 curriculum, and the basics of the year 10 curriculum, you should be able to run through it without too much trouble. (Study up on things like Pressure, and a tiny bit of biology, those questions tripped me up a bit.)
Next, there's a Mathematics exam, which is your basic year 10 and fundamental year 9 mathematics, if you get an average of 80% on your tests, don't worry, otherwise just study up on the things you've learned so far.
Verbal reasoning, and English Comprehension will also be on the test
EBSS Uses EduTest as their test hoster, so the tests will be under their format.
https://www.edutest.com.au/Edutest/LoginCustomer.aspYou'll have to pay for practice tests, but these help A LOT.
Once again, don't worry about it. I'm year 9 currently, I did the test this year, got 3 superiors, and was offered a spot in Year 11 next year, allowing me to skip Year 10! Like I said, easy. I'm going to JMSS with GodlyBuddha.

Good luck!
Show interest, and don't forget to practice, practice, and watch anime- I mean, practice.