The Responsible Serving of Alcohol (RSA) certificate allows you to serve alcohol in licensed establishments in the state that it was issued in. Every Australian state has different RSA requirements, so if you move states you'll need to get a new certificate.
Almost all jobs that involve alcohol require you to have one, so it's worth doing. I just googled for "RSA Melbourne" and chose one of the courses. It cost $39 and lasted four hours. There was a test at the end, with a pass rate of 70%, but no one failed, and they had everyone's certificates printed before the course had even started. It's that kind of course.
Having it definitely came in handy when I was job-hunting. It went straight on my resume and was just another thing I could (truthfully) say yes to in interviews.