What are they even fighting for in the first place? Why are we fighting Syria?
We as a country aren't fighting in Syria, they went over as individuals (and i guess volunteers).
Most of them seem to be fighting against the current government/Assad. Within the side fighting
against the government, there are different organisations. Some like the free syrian army are just fed up with Assads dictatorship and other issues like that. There are also radical islamist organisations, they dont like Assad much either but thats because he's more of a moderate muslim (and not the same kind as them either). They want to capture Syria and have it under Sharia law. Most of the news stories seem to indicate that most of the Australians going over (and indeed foreign fighters in general) are fighting for the radical islamists.
Whilst it might be confusing, the islamists and the free syrian army had a tenuous (but obviously uncomfortable) alliance for a decent amount of time. Recently exploded and now they're also fighting each-other
AND Assad/the Syrian government.