"I will go to Australia."
Translation:Εγώ θα πάω στην Αυστραλία.
Θα πηγαίνω = I will be going, Μέλλοντας Εξακολουθητικός (Future Continuous)
Θα πάω = I will go, Μέλλοντας Στιγμιαίος (Future Simple).
It's a tense difference. ^.^
Nothing. That's one of the accepted alternatives.
(Well, with capital Θα at the beginning of the sentence, but that shouldn't make a difference in whether it was accepted or not.)